How can I concatenate (merge, combine) two values?
For example I have:
tmp = cbind("GAD", "AB")
tmp
# [,1] [,2]
# [1,] "GAD" "AB"
My goal is to concatenate the two values in "tmp" to one string:
tmp_new = "GAD,AB"
Which function can do this for me?
paste()
is the way to go. As the previous posters pointed out, paste can do two things:
concatenate values into one "string", e.g.
> paste("Hello", "world", sep=" ")
[1] "Hello world"
where the argument sep specifies the character(s) to be used between the arguments to concatenate,
or collapse character vectors
> x <- c("Hello", "World")
> x
[1] "Hello" "World"
> paste(x, collapse="--")
[1] "Hello--World"
where the argument collapse specifies the character(s) to be used between the elements of the vector to be collapsed.
You can even combine both:
> paste(x, "and some more", sep="|-|", collapse="--")
[1] "Hello|-|and some more--World|-|and some more"
help.search() is a handy function, e.g.
> help.search("concatenate")
will lead you to paste().
For the first non-paste() answer, we can look at stringr::str_c() (and then toString() below). It hasn't been around as long as this question, so I think it's useful to mention that it also exists.
Very simple to use, as you can see.
tmp <- cbind("GAD", "AB")
library(stringr)
str_c(tmp, collapse = ",")
# [1] "GAD,AB"
From its documentation file description, it fits this problem nicely.
To understand how str_c works, you need to imagine that you are building up a matrix of strings. Each input argument forms a column, and is expanded to the length of the longest argument, using the usual recyling rules. The sep string is inserted between each column. If collapse is NULL each row is collapsed into a single string. If non-NULL that string is inserted at the end of each row, and the entire matrix collapsed to a single string.
Added 4/13/2016: It's not exactly the same as your desired output (extra space), but no one has mentioned it either. toString() is basically a version of paste() with collapse = ", " hard-coded, so you can do
toString(tmp)
# [1] "GAD, AB"
As others have pointed out, paste() is the way to go. But it can get annoying to have to type paste(str1, str2, str3, sep='') everytime you want the non-default separator.
You can very easily create wrapper functions that make life much simpler. For instance, if you find yourself concatenating strings with no separator really often, you can do:
p <- function(..., sep='') {
paste(..., sep=sep, collapse=sep)
}
or if you often want to join strings from a vector (like implode() from PHP):
implode <- function(..., sep='') {
paste(..., collapse=sep)
}
Allows you do do this:
p('a', 'b', 'c')
#[1] "abc"
vec <- c('a', 'b', 'c')
implode(vec)
#[1] "abc"
implode(vec, sep=', ')
#[1] "a, b, c"
Also, there is the built-in paste0, which does the same thing as my implode, but without allowing custom separators. It's slightly more efficient than paste().
> tmp = paste("GAD", "AB", sep = ",")
> tmp
[1] "GAD,AB"
I found this from Google by searching for R concatenate strings: http://stat.ethz.ch/R-manual/R-patched/library/base/html/paste.html
Alternatively, if your objective is to output directly to a file or stdout, you can use cat:
cat(s1, s2, sep=", ")
Another way:
sprintf("%s you can add other static strings here %s",string1,string2)
It sometimes useful than paste() function. %s denotes the place where the subjective strings will be included.
Note that this will come in handy as you try to build a path:
sprintf("/%s", paste("this", "is", "a", "path", sep="/"))
output
/this/is/a/path
You can create you own operator :
'%&%' <- function(x, y)paste0(x,y)
"new" %&% "operator"
[1] newoperator`
You can also redefine 'and' (&) operator :
'&' <- function(x, y)paste0(x,y)
"dirty" & "trick"
"dirtytrick"
messing with baseline syntax is ugly, but so is using paste()/paste0() if you work only with your own code you can (almost always) replace logical & and operator with * and do multiplication of logical values instead of using logical 'and &'
Given the matrix, tmp, that you created:
paste(tmp[1,], collapse = ",")
I assume there is some reason why you're creating a matrix using cbind, as opposed to simply:
tmp <- "GAD,AB"
Consider the case where the strings are columns and the result should be a new column:
df <- data.frame(a = letters[1:5], b = LETTERS[1:5], c = 1:5)
df$new_col <- do.call(paste, c(df[c("a", "b")], sep = ", "))
df
# a b c new_col
#1 a A 1 a, A
#2 b B 2 b, B
#3 c C 3 c, C
#4 d D 4 d, D
#5 e E 5 e, E
Optionally, skip the [c("a", "b")] subsetting if all columns needs to be pasted.
# you can also try str_c from stringr package as mentioned by other users too!
do.call(str_c, c(df[c("a", "b")], sep = ", "))
glue is a new function, data class, and package that has been developed as part of the tidyverse, with a lot of extended functionality. It combines features from paste, sprintf, and the previous other answers.
tmp <- tibble::tibble(firststring = "GAD", secondstring = "AB")
(tmp_new <- glue::glue_data(tmp, "{firststring},{secondstring}"))
#> GAD,AB
Created on 2019-03-06 by the reprex package (v0.2.1)
Yes, it's overkill for the simple example in this question, but powerful for many situations. (see https://glue.tidyverse.org/)
Quick example compared to paste with with below. The glue code was a bit easier to type and looks a bit easier to read.
tmp <- tibble::tibble(firststring = c("GAD", "GAD2", "GAD3"), secondstring = c("AB1", "AB2", "AB3"))
(tmp_new <- glue::glue_data(tmp, "{firststring} and {secondstring} went to the park for a walk. {firststring} forgot his keys."))
#> GAD and AB1 went to the park for a walk. GAD forgot his keys.
#> GAD2 and AB2 went to the park for a walk. GAD2 forgot his keys.
#> GAD3 and AB3 went to the park for a walk. GAD3 forgot his keys.
(with(tmp, paste(firststring, "and", secondstring, "went to the park for a walk.", firststring, "forgot his keys.")))
#> [1] "GAD and AB1 went to the park for a walk. GAD forgot his keys."
#> [2] "GAD2 and AB2 went to the park for a walk. GAD2 forgot his keys."
#> [3] "GAD3 and AB3 went to the park for a walk. GAD3 forgot his keys."
Created on 2019-03-06 by the reprex package (v0.2.1)
Another non-paste answer:
x <- capture.output(cat(data, sep = ","))
x
[1] "GAD,AB"
Where
data <- c("GAD", "AB")
Related
How can I concatenate (merge, combine) two values?
For example I have:
tmp = cbind("GAD", "AB")
tmp
# [,1] [,2]
# [1,] "GAD" "AB"
My goal is to concatenate the two values in "tmp" to one string:
tmp_new = "GAD,AB"
Which function can do this for me?
paste()
is the way to go. As the previous posters pointed out, paste can do two things:
concatenate values into one "string", e.g.
> paste("Hello", "world", sep=" ")
[1] "Hello world"
where the argument sep specifies the character(s) to be used between the arguments to concatenate,
or collapse character vectors
> x <- c("Hello", "World")
> x
[1] "Hello" "World"
> paste(x, collapse="--")
[1] "Hello--World"
where the argument collapse specifies the character(s) to be used between the elements of the vector to be collapsed.
You can even combine both:
> paste(x, "and some more", sep="|-|", collapse="--")
[1] "Hello|-|and some more--World|-|and some more"
help.search() is a handy function, e.g.
> help.search("concatenate")
will lead you to paste().
For the first non-paste() answer, we can look at stringr::str_c() (and then toString() below). It hasn't been around as long as this question, so I think it's useful to mention that it also exists.
Very simple to use, as you can see.
tmp <- cbind("GAD", "AB")
library(stringr)
str_c(tmp, collapse = ",")
# [1] "GAD,AB"
From its documentation file description, it fits this problem nicely.
To understand how str_c works, you need to imagine that you are building up a matrix of strings. Each input argument forms a column, and is expanded to the length of the longest argument, using the usual recyling rules. The sep string is inserted between each column. If collapse is NULL each row is collapsed into a single string. If non-NULL that string is inserted at the end of each row, and the entire matrix collapsed to a single string.
Added 4/13/2016: It's not exactly the same as your desired output (extra space), but no one has mentioned it either. toString() is basically a version of paste() with collapse = ", " hard-coded, so you can do
toString(tmp)
# [1] "GAD, AB"
As others have pointed out, paste() is the way to go. But it can get annoying to have to type paste(str1, str2, str3, sep='') everytime you want the non-default separator.
You can very easily create wrapper functions that make life much simpler. For instance, if you find yourself concatenating strings with no separator really often, you can do:
p <- function(..., sep='') {
paste(..., sep=sep, collapse=sep)
}
or if you often want to join strings from a vector (like implode() from PHP):
implode <- function(..., sep='') {
paste(..., collapse=sep)
}
Allows you do do this:
p('a', 'b', 'c')
#[1] "abc"
vec <- c('a', 'b', 'c')
implode(vec)
#[1] "abc"
implode(vec, sep=', ')
#[1] "a, b, c"
Also, there is the built-in paste0, which does the same thing as my implode, but without allowing custom separators. It's slightly more efficient than paste().
> tmp = paste("GAD", "AB", sep = ",")
> tmp
[1] "GAD,AB"
I found this from Google by searching for R concatenate strings: http://stat.ethz.ch/R-manual/R-patched/library/base/html/paste.html
Alternatively, if your objective is to output directly to a file or stdout, you can use cat:
cat(s1, s2, sep=", ")
Another way:
sprintf("%s you can add other static strings here %s",string1,string2)
It sometimes useful than paste() function. %s denotes the place where the subjective strings will be included.
Note that this will come in handy as you try to build a path:
sprintf("/%s", paste("this", "is", "a", "path", sep="/"))
output
/this/is/a/path
You can create you own operator :
'%&%' <- function(x, y)paste0(x,y)
"new" %&% "operator"
[1] newoperator`
You can also redefine 'and' (&) operator :
'&' <- function(x, y)paste0(x,y)
"dirty" & "trick"
"dirtytrick"
messing with baseline syntax is ugly, but so is using paste()/paste0() if you work only with your own code you can (almost always) replace logical & and operator with * and do multiplication of logical values instead of using logical 'and &'
Given the matrix, tmp, that you created:
paste(tmp[1,], collapse = ",")
I assume there is some reason why you're creating a matrix using cbind, as opposed to simply:
tmp <- "GAD,AB"
Consider the case where the strings are columns and the result should be a new column:
df <- data.frame(a = letters[1:5], b = LETTERS[1:5], c = 1:5)
df$new_col <- do.call(paste, c(df[c("a", "b")], sep = ", "))
df
# a b c new_col
#1 a A 1 a, A
#2 b B 2 b, B
#3 c C 3 c, C
#4 d D 4 d, D
#5 e E 5 e, E
Optionally, skip the [c("a", "b")] subsetting if all columns needs to be pasted.
# you can also try str_c from stringr package as mentioned by other users too!
do.call(str_c, c(df[c("a", "b")], sep = ", "))
glue is a new function, data class, and package that has been developed as part of the tidyverse, with a lot of extended functionality. It combines features from paste, sprintf, and the previous other answers.
tmp <- tibble::tibble(firststring = "GAD", secondstring = "AB")
(tmp_new <- glue::glue_data(tmp, "{firststring},{secondstring}"))
#> GAD,AB
Created on 2019-03-06 by the reprex package (v0.2.1)
Yes, it's overkill for the simple example in this question, but powerful for many situations. (see https://glue.tidyverse.org/)
Quick example compared to paste with with below. The glue code was a bit easier to type and looks a bit easier to read.
tmp <- tibble::tibble(firststring = c("GAD", "GAD2", "GAD3"), secondstring = c("AB1", "AB2", "AB3"))
(tmp_new <- glue::glue_data(tmp, "{firststring} and {secondstring} went to the park for a walk. {firststring} forgot his keys."))
#> GAD and AB1 went to the park for a walk. GAD forgot his keys.
#> GAD2 and AB2 went to the park for a walk. GAD2 forgot his keys.
#> GAD3 and AB3 went to the park for a walk. GAD3 forgot his keys.
(with(tmp, paste(firststring, "and", secondstring, "went to the park for a walk.", firststring, "forgot his keys.")))
#> [1] "GAD and AB1 went to the park for a walk. GAD forgot his keys."
#> [2] "GAD2 and AB2 went to the park for a walk. GAD2 forgot his keys."
#> [3] "GAD3 and AB3 went to the park for a walk. GAD3 forgot his keys."
Created on 2019-03-06 by the reprex package (v0.2.1)
Another non-paste answer:
x <- capture.output(cat(data, sep = ","))
x
[1] "GAD,AB"
Where
data <- c("GAD", "AB")
I'm trying to teach myself R and in doing some sample problems I came across the need to reverse a string.
Here's what I've tried so far but the paste operation doesn't seem to have any effect.
There must be something I'm not understanding about lists? (I also don't understand why I need the [[1]] after strsplit.)
test <- strsplit("greg", NULL)[[1]]
test
# [1] "g" "r" "e" "g"
test_rev <- rev(test)
test_rev
# [1] "g" "e" "r" "g"
paste(test_rev)
# [1] "g" "e" "r" "g"
From ?strsplit, a function that'll reverse every string in a vector of strings:
## a useful function: rev() for strings
strReverse <- function(x)
sapply(lapply(strsplit(x, NULL), rev), paste, collapse="")
strReverse(c("abc", "Statistics"))
# [1] "cba" "scitsitatS"
stringi has had this function for quite a long time:
stringi::stri_reverse("abcdef")
## [1] "fedcba"
Also note that it's vectorized:
stringi::stri_reverse(c("a", "ab", "abc"))
## [1] "a" "ba" "cba"
As #mplourde points out, you want the collapse argument:
paste(test_rev, collapse='')
Most commands in R are vectorized, but how exactly the command handles vectors depends on the command. paste will operate over multiple vectors, combining the ith element of each:
> paste(letters[1:5],letters[1:5])
[1] "a a" "b b" "c c" "d d" "e e"
collapse tells it to operate within a vector instead.
The following can be a useful way to reverse a vector of strings x, and is slightly faster (and more memory efficient) because it avoids generating a list (as in using strsplit):
x <- rep( paste( collapse="", LETTERS ), 100 )
str_rev <- function(x) {
sapply( x, function(xx) {
intToUtf8( rev( utf8ToInt( xx ) ) )
} )
}
str_rev(x)
If you know that you're going to be working with ASCII characters and speed matters, there is a fast C implementation for reversing a vector of strings built into Kmisc:
install.packages("Kmisc")
str_rev(x)
You can also use the IRanges package.
library(IRanges)
x <- "ATGCSDS"
reverse(x)
# [1] "SDSCGTA"
You can also use the Biostrings package.
library(Biostrings)
x <- "ATGCSDS"
reverse(x)
# [1] "SDSCGTA"
If your data is in a data.frame, you can use sqldf:
myStrings <- data.frame(forward = c("does", "this", "actually", "work"))
library(sqldf)
sqldf("select forward, reverse(forward) `reverse` from myStrings")
# forward reverse
# 1 does seod
# 2 this siht
# 3 actually yllautca
# 4 work krow
Here is a function that returns the whole reversed string, or optionally the reverse string keeping only the elements specified by index, counting backward from the last character.
revString = function(string, index = 1:nchar(string)){
paste(rev(unlist(strsplit(string, NULL)))[index], collapse = "")
}
First, define an easily recognizable string as an example:
(myString <- paste(letters, collapse = ""))
[1] "abcdefghijklmnopqrstuvwxyz"
Now try out the function revString with and without the index:
revString(myString)
[1] "zyxwvutsrqponmlkjihgfedcba"
revString(myString, 1:5)
[1] "zyxwv"
The easiest way to reverse string:
#reverse string----------------------------------------------------------------
revString <- function(text){
paste(rev(unlist(strsplit(text,NULL))),collapse="")
}
#example:
revString("abcdef")
You can do with rev() function as mentioned in a previous post.
`X <- "MyString"
RevX <- paste(rev(unlist(strsplit(X,NULL))),collapse="")
Output : "gnirtSyM"
Thanks,
Here's a solution with gsub. Although I agree that it's easier with strsplit and paste (as pointed out in the other answers), it may be interesting to see that it works with regular expressions too:
test <- "greg"
n <- nchar(test) # the number of characters in the string
gsub(paste(rep("(.)", n), collapse = ""),
paste("", seq(n, 1), sep = "\\", collapse = ""),
test)
# [1] "gerg"
##function to reverse the given word or sentence
reverse <- function(mystring){
n <- nchar(mystring)
revstring <- rep(NA, n)
b <- n:1
c <- rev(b)
for (i in 1:n) {
revstring[i] <- substr(mystring,c[(n+1)- i], b[i])
}
newrevstring <- paste(revstring, sep = "", collapse = "")
return (cat("your string =", mystring, "\n",
("reverse letters = "), revstring, "\n",
"reverse string =", newrevstring,"\n"))
}
Here is one more base-R solution:
# Define function
strrev <- function(x) {
nc <- nchar(x)
paste(substring(x, nc:1, nc:1), collapse = "")
}
# Example
strrev("Sore was I ere I saw Eros")
[1] "sorE was I ere I saw eroS"
Solution was inspired by these U. Auckland slides.
The following Code will take input from user and reverse the entire string-
revstring=function(s)
print(paste(rev(strsplit(s,"")[[1]]),collapse=""))
str=readline("Enter the string:")
revstring(str)
So apparently front-end JS developers get asked to do this (for interviews) in JS without using built-in reverse functions. It took me a few minutes, but I came up with:
string <- 'hello'
foo <- vector()
for (i in nchar(string):1) foo <- append(foo,unlist(strsplit(string,''))[i])
paste0(foo,collapse='')
Which all could be wrapped in a function...
What about higher-order functionals? Reduce?
I'm trying to teach myself R and in doing some sample problems I came across the need to reverse a string.
Here's what I've tried so far but the paste operation doesn't seem to have any effect.
There must be something I'm not understanding about lists? (I also don't understand why I need the [[1]] after strsplit.)
test <- strsplit("greg", NULL)[[1]]
test
# [1] "g" "r" "e" "g"
test_rev <- rev(test)
test_rev
# [1] "g" "e" "r" "g"
paste(test_rev)
# [1] "g" "e" "r" "g"
From ?strsplit, a function that'll reverse every string in a vector of strings:
## a useful function: rev() for strings
strReverse <- function(x)
sapply(lapply(strsplit(x, NULL), rev), paste, collapse="")
strReverse(c("abc", "Statistics"))
# [1] "cba" "scitsitatS"
stringi has had this function for quite a long time:
stringi::stri_reverse("abcdef")
## [1] "fedcba"
Also note that it's vectorized:
stringi::stri_reverse(c("a", "ab", "abc"))
## [1] "a" "ba" "cba"
As #mplourde points out, you want the collapse argument:
paste(test_rev, collapse='')
Most commands in R are vectorized, but how exactly the command handles vectors depends on the command. paste will operate over multiple vectors, combining the ith element of each:
> paste(letters[1:5],letters[1:5])
[1] "a a" "b b" "c c" "d d" "e e"
collapse tells it to operate within a vector instead.
The following can be a useful way to reverse a vector of strings x, and is slightly faster (and more memory efficient) because it avoids generating a list (as in using strsplit):
x <- rep( paste( collapse="", LETTERS ), 100 )
str_rev <- function(x) {
sapply( x, function(xx) {
intToUtf8( rev( utf8ToInt( xx ) ) )
} )
}
str_rev(x)
If you know that you're going to be working with ASCII characters and speed matters, there is a fast C implementation for reversing a vector of strings built into Kmisc:
install.packages("Kmisc")
str_rev(x)
You can also use the IRanges package.
library(IRanges)
x <- "ATGCSDS"
reverse(x)
# [1] "SDSCGTA"
You can also use the Biostrings package.
library(Biostrings)
x <- "ATGCSDS"
reverse(x)
# [1] "SDSCGTA"
If your data is in a data.frame, you can use sqldf:
myStrings <- data.frame(forward = c("does", "this", "actually", "work"))
library(sqldf)
sqldf("select forward, reverse(forward) `reverse` from myStrings")
# forward reverse
# 1 does seod
# 2 this siht
# 3 actually yllautca
# 4 work krow
Here is a function that returns the whole reversed string, or optionally the reverse string keeping only the elements specified by index, counting backward from the last character.
revString = function(string, index = 1:nchar(string)){
paste(rev(unlist(strsplit(string, NULL)))[index], collapse = "")
}
First, define an easily recognizable string as an example:
(myString <- paste(letters, collapse = ""))
[1] "abcdefghijklmnopqrstuvwxyz"
Now try out the function revString with and without the index:
revString(myString)
[1] "zyxwvutsrqponmlkjihgfedcba"
revString(myString, 1:5)
[1] "zyxwv"
The easiest way to reverse string:
#reverse string----------------------------------------------------------------
revString <- function(text){
paste(rev(unlist(strsplit(text,NULL))),collapse="")
}
#example:
revString("abcdef")
You can do with rev() function as mentioned in a previous post.
`X <- "MyString"
RevX <- paste(rev(unlist(strsplit(X,NULL))),collapse="")
Output : "gnirtSyM"
Thanks,
Here's a solution with gsub. Although I agree that it's easier with strsplit and paste (as pointed out in the other answers), it may be interesting to see that it works with regular expressions too:
test <- "greg"
n <- nchar(test) # the number of characters in the string
gsub(paste(rep("(.)", n), collapse = ""),
paste("", seq(n, 1), sep = "\\", collapse = ""),
test)
# [1] "gerg"
##function to reverse the given word or sentence
reverse <- function(mystring){
n <- nchar(mystring)
revstring <- rep(NA, n)
b <- n:1
c <- rev(b)
for (i in 1:n) {
revstring[i] <- substr(mystring,c[(n+1)- i], b[i])
}
newrevstring <- paste(revstring, sep = "", collapse = "")
return (cat("your string =", mystring, "\n",
("reverse letters = "), revstring, "\n",
"reverse string =", newrevstring,"\n"))
}
Here is one more base-R solution:
# Define function
strrev <- function(x) {
nc <- nchar(x)
paste(substring(x, nc:1, nc:1), collapse = "")
}
# Example
strrev("Sore was I ere I saw Eros")
[1] "sorE was I ere I saw eroS"
Solution was inspired by these U. Auckland slides.
The following Code will take input from user and reverse the entire string-
revstring=function(s)
print(paste(rev(strsplit(s,"")[[1]]),collapse=""))
str=readline("Enter the string:")
revstring(str)
So apparently front-end JS developers get asked to do this (for interviews) in JS without using built-in reverse functions. It took me a few minutes, but I came up with:
string <- 'hello'
foo <- vector()
for (i in nchar(string):1) foo <- append(foo,unlist(strsplit(string,''))[i])
paste0(foo,collapse='')
Which all could be wrapped in a function...
What about higher-order functionals? Reduce?
I'm trying to teach myself R and in doing some sample problems I came across the need to reverse a string.
Here's what I've tried so far but the paste operation doesn't seem to have any effect.
There must be something I'm not understanding about lists? (I also don't understand why I need the [[1]] after strsplit.)
test <- strsplit("greg", NULL)[[1]]
test
# [1] "g" "r" "e" "g"
test_rev <- rev(test)
test_rev
# [1] "g" "e" "r" "g"
paste(test_rev)
# [1] "g" "e" "r" "g"
From ?strsplit, a function that'll reverse every string in a vector of strings:
## a useful function: rev() for strings
strReverse <- function(x)
sapply(lapply(strsplit(x, NULL), rev), paste, collapse="")
strReverse(c("abc", "Statistics"))
# [1] "cba" "scitsitatS"
stringi has had this function for quite a long time:
stringi::stri_reverse("abcdef")
## [1] "fedcba"
Also note that it's vectorized:
stringi::stri_reverse(c("a", "ab", "abc"))
## [1] "a" "ba" "cba"
As #mplourde points out, you want the collapse argument:
paste(test_rev, collapse='')
Most commands in R are vectorized, but how exactly the command handles vectors depends on the command. paste will operate over multiple vectors, combining the ith element of each:
> paste(letters[1:5],letters[1:5])
[1] "a a" "b b" "c c" "d d" "e e"
collapse tells it to operate within a vector instead.
The following can be a useful way to reverse a vector of strings x, and is slightly faster (and more memory efficient) because it avoids generating a list (as in using strsplit):
x <- rep( paste( collapse="", LETTERS ), 100 )
str_rev <- function(x) {
sapply( x, function(xx) {
intToUtf8( rev( utf8ToInt( xx ) ) )
} )
}
str_rev(x)
If you know that you're going to be working with ASCII characters and speed matters, there is a fast C implementation for reversing a vector of strings built into Kmisc:
install.packages("Kmisc")
str_rev(x)
You can also use the IRanges package.
library(IRanges)
x <- "ATGCSDS"
reverse(x)
# [1] "SDSCGTA"
You can also use the Biostrings package.
library(Biostrings)
x <- "ATGCSDS"
reverse(x)
# [1] "SDSCGTA"
If your data is in a data.frame, you can use sqldf:
myStrings <- data.frame(forward = c("does", "this", "actually", "work"))
library(sqldf)
sqldf("select forward, reverse(forward) `reverse` from myStrings")
# forward reverse
# 1 does seod
# 2 this siht
# 3 actually yllautca
# 4 work krow
Here is a function that returns the whole reversed string, or optionally the reverse string keeping only the elements specified by index, counting backward from the last character.
revString = function(string, index = 1:nchar(string)){
paste(rev(unlist(strsplit(string, NULL)))[index], collapse = "")
}
First, define an easily recognizable string as an example:
(myString <- paste(letters, collapse = ""))
[1] "abcdefghijklmnopqrstuvwxyz"
Now try out the function revString with and without the index:
revString(myString)
[1] "zyxwvutsrqponmlkjihgfedcba"
revString(myString, 1:5)
[1] "zyxwv"
The easiest way to reverse string:
#reverse string----------------------------------------------------------------
revString <- function(text){
paste(rev(unlist(strsplit(text,NULL))),collapse="")
}
#example:
revString("abcdef")
You can do with rev() function as mentioned in a previous post.
`X <- "MyString"
RevX <- paste(rev(unlist(strsplit(X,NULL))),collapse="")
Output : "gnirtSyM"
Thanks,
Here's a solution with gsub. Although I agree that it's easier with strsplit and paste (as pointed out in the other answers), it may be interesting to see that it works with regular expressions too:
test <- "greg"
n <- nchar(test) # the number of characters in the string
gsub(paste(rep("(.)", n), collapse = ""),
paste("", seq(n, 1), sep = "\\", collapse = ""),
test)
# [1] "gerg"
##function to reverse the given word or sentence
reverse <- function(mystring){
n <- nchar(mystring)
revstring <- rep(NA, n)
b <- n:1
c <- rev(b)
for (i in 1:n) {
revstring[i] <- substr(mystring,c[(n+1)- i], b[i])
}
newrevstring <- paste(revstring, sep = "", collapse = "")
return (cat("your string =", mystring, "\n",
("reverse letters = "), revstring, "\n",
"reverse string =", newrevstring,"\n"))
}
Here is one more base-R solution:
# Define function
strrev <- function(x) {
nc <- nchar(x)
paste(substring(x, nc:1, nc:1), collapse = "")
}
# Example
strrev("Sore was I ere I saw Eros")
[1] "sorE was I ere I saw eroS"
Solution was inspired by these U. Auckland slides.
The following Code will take input from user and reverse the entire string-
revstring=function(s)
print(paste(rev(strsplit(s,"")[[1]]),collapse=""))
str=readline("Enter the string:")
revstring(str)
So apparently front-end JS developers get asked to do this (for interviews) in JS without using built-in reverse functions. It took me a few minutes, but I came up with:
string <- 'hello'
foo <- vector()
for (i in nchar(string):1) foo <- append(foo,unlist(strsplit(string,''))[i])
paste0(foo,collapse='')
Which all could be wrapped in a function...
What about higher-order functionals? Reduce?
How can I concatenate (merge, combine) two values?
For example I have:
tmp = cbind("GAD", "AB")
tmp
# [,1] [,2]
# [1,] "GAD" "AB"
My goal is to concatenate the two values in "tmp" to one string:
tmp_new = "GAD,AB"
Which function can do this for me?
paste()
is the way to go. As the previous posters pointed out, paste can do two things:
concatenate values into one "string", e.g.
> paste("Hello", "world", sep=" ")
[1] "Hello world"
where the argument sep specifies the character(s) to be used between the arguments to concatenate,
or collapse character vectors
> x <- c("Hello", "World")
> x
[1] "Hello" "World"
> paste(x, collapse="--")
[1] "Hello--World"
where the argument collapse specifies the character(s) to be used between the elements of the vector to be collapsed.
You can even combine both:
> paste(x, "and some more", sep="|-|", collapse="--")
[1] "Hello|-|and some more--World|-|and some more"
help.search() is a handy function, e.g.
> help.search("concatenate")
will lead you to paste().
For the first non-paste() answer, we can look at stringr::str_c() (and then toString() below). It hasn't been around as long as this question, so I think it's useful to mention that it also exists.
Very simple to use, as you can see.
tmp <- cbind("GAD", "AB")
library(stringr)
str_c(tmp, collapse = ",")
# [1] "GAD,AB"
From its documentation file description, it fits this problem nicely.
To understand how str_c works, you need to imagine that you are building up a matrix of strings. Each input argument forms a column, and is expanded to the length of the longest argument, using the usual recyling rules. The sep string is inserted between each column. If collapse is NULL each row is collapsed into a single string. If non-NULL that string is inserted at the end of each row, and the entire matrix collapsed to a single string.
Added 4/13/2016: It's not exactly the same as your desired output (extra space), but no one has mentioned it either. toString() is basically a version of paste() with collapse = ", " hard-coded, so you can do
toString(tmp)
# [1] "GAD, AB"
As others have pointed out, paste() is the way to go. But it can get annoying to have to type paste(str1, str2, str3, sep='') everytime you want the non-default separator.
You can very easily create wrapper functions that make life much simpler. For instance, if you find yourself concatenating strings with no separator really often, you can do:
p <- function(..., sep='') {
paste(..., sep=sep, collapse=sep)
}
or if you often want to join strings from a vector (like implode() from PHP):
implode <- function(..., sep='') {
paste(..., collapse=sep)
}
Allows you do do this:
p('a', 'b', 'c')
#[1] "abc"
vec <- c('a', 'b', 'c')
implode(vec)
#[1] "abc"
implode(vec, sep=', ')
#[1] "a, b, c"
Also, there is the built-in paste0, which does the same thing as my implode, but without allowing custom separators. It's slightly more efficient than paste().
> tmp = paste("GAD", "AB", sep = ",")
> tmp
[1] "GAD,AB"
I found this from Google by searching for R concatenate strings: http://stat.ethz.ch/R-manual/R-patched/library/base/html/paste.html
Alternatively, if your objective is to output directly to a file or stdout, you can use cat:
cat(s1, s2, sep=", ")
Another way:
sprintf("%s you can add other static strings here %s",string1,string2)
It sometimes useful than paste() function. %s denotes the place where the subjective strings will be included.
Note that this will come in handy as you try to build a path:
sprintf("/%s", paste("this", "is", "a", "path", sep="/"))
output
/this/is/a/path
You can create you own operator :
'%&%' <- function(x, y)paste0(x,y)
"new" %&% "operator"
[1] newoperator`
You can also redefine 'and' (&) operator :
'&' <- function(x, y)paste0(x,y)
"dirty" & "trick"
"dirtytrick"
messing with baseline syntax is ugly, but so is using paste()/paste0() if you work only with your own code you can (almost always) replace logical & and operator with * and do multiplication of logical values instead of using logical 'and &'
Given the matrix, tmp, that you created:
paste(tmp[1,], collapse = ",")
I assume there is some reason why you're creating a matrix using cbind, as opposed to simply:
tmp <- "GAD,AB"
Consider the case where the strings are columns and the result should be a new column:
df <- data.frame(a = letters[1:5], b = LETTERS[1:5], c = 1:5)
df$new_col <- do.call(paste, c(df[c("a", "b")], sep = ", "))
df
# a b c new_col
#1 a A 1 a, A
#2 b B 2 b, B
#3 c C 3 c, C
#4 d D 4 d, D
#5 e E 5 e, E
Optionally, skip the [c("a", "b")] subsetting if all columns needs to be pasted.
# you can also try str_c from stringr package as mentioned by other users too!
do.call(str_c, c(df[c("a", "b")], sep = ", "))
glue is a new function, data class, and package that has been developed as part of the tidyverse, with a lot of extended functionality. It combines features from paste, sprintf, and the previous other answers.
tmp <- tibble::tibble(firststring = "GAD", secondstring = "AB")
(tmp_new <- glue::glue_data(tmp, "{firststring},{secondstring}"))
#> GAD,AB
Created on 2019-03-06 by the reprex package (v0.2.1)
Yes, it's overkill for the simple example in this question, but powerful for many situations. (see https://glue.tidyverse.org/)
Quick example compared to paste with with below. The glue code was a bit easier to type and looks a bit easier to read.
tmp <- tibble::tibble(firststring = c("GAD", "GAD2", "GAD3"), secondstring = c("AB1", "AB2", "AB3"))
(tmp_new <- glue::glue_data(tmp, "{firststring} and {secondstring} went to the park for a walk. {firststring} forgot his keys."))
#> GAD and AB1 went to the park for a walk. GAD forgot his keys.
#> GAD2 and AB2 went to the park for a walk. GAD2 forgot his keys.
#> GAD3 and AB3 went to the park for a walk. GAD3 forgot his keys.
(with(tmp, paste(firststring, "and", secondstring, "went to the park for a walk.", firststring, "forgot his keys.")))
#> [1] "GAD and AB1 went to the park for a walk. GAD forgot his keys."
#> [2] "GAD2 and AB2 went to the park for a walk. GAD2 forgot his keys."
#> [3] "GAD3 and AB3 went to the park for a walk. GAD3 forgot his keys."
Created on 2019-03-06 by the reprex package (v0.2.1)
Another non-paste answer:
x <- capture.output(cat(data, sep = ","))
x
[1] "GAD,AB"
Where
data <- c("GAD", "AB")