I'm trying to find this specific character "|" location in a string.
for example: 8,75.2|6,0.376
the answer I expect is 7
I trying to use regexpr:
regexpr('|',"8,75.2|6,0.376")
but it didn't worked (although it did work to when I looked for the ",")
any ideas?
The '|' character is a special character in regular expression. You can search for a '|' by using the escape character '\' regexpr("\\|","8,75.2|6,0.376")
Another option is to use lapply:
> str <- '8,75.2|6,0.376'
> chars <- strsplit(str, '')
> chars
[[1]]
[1] "8" "," "7" "5" "." "2" "|" "6" "," "0" "." "3" "7" "6"
> loc <- lapply(chars, function(elem) which (elem == '|'))
> loc
[[1]]
[1] 7
See the lapply documentation
You can use the stringr package:
library(stringr)
str_locate("8,75.2|6,0.376",fixed('|'))
#or
str_locate("8,75.2|6,0.376",'\\|')
sample result:
start end
[1,] 7 7
Related
I am trying to match the last digit in a character vector and replace it with the matched digit - 1. I have believe gsub is what I need to use but I cannot figure out what to use as the 'replace' argument. I can match the last number using:
gsub('[0-9]$', ???, chrvector)
But I am not sure how to replace the matched number with itself - 1.
Any help would be much appreciated.
Thank you.
We can do this easily with gsubfn
library(gsubfn)
gsubfn("([0-9]+)", ~as.numeric(x)-1, chrvector)
#[1] "str97" "v197exdf"
Or for the last digit
gsubfn("([0-9])([^0-9]*)$", ~paste0(as.numeric(x)-1, y), chrvector2)
#[1] "str97" "v197exdf" "v33chr138d"
data
chrvector <- c("str98", "v198exdf")
chrvector2 <- c("str98", "v198exdf", "v33chr139d")
Assuming the last digit is not zero,
chrvector <- as.character(1:5)
chrvector
#[1] "1" "2" "3" "4" "5"
chrvector <- paste(chrvector, collapse='') # convert to character string
chrvector <- paste0(substring(chrvector,1, nchar(chrvector)-1), as.integer(gsub('.*([0-9])$', '\\1', chrvector))-1)
unlist(strsplit(chrvector, split=''))
# [1] "1" "2" "3" "4" "4"
This works even if you have the last digit zero:
chrvector <- c(as.character(1:4), '0') # [1] "1" "2" "3" "4" "0"
chrvector <- paste(chrvector, collapse='')
chrvector <- as.character(as.integer(chrvector)-1)
unlist(strsplit(chrvector, split=''))
# [1] "1" "2" "3" "3" "9"
I want to get all characters that are ahead of the first "." if there is one. Otherwise, I want to get back the same character ("8" -> "8").
Example:
v<-c("7.7.4","8","12.6","11.5.2.1")
I want to get something like this:
[1] "7 "8" "12" "11"
My idea was to split each element at "." and then only take the first split. I found no solution that worked...
You can use sub
sub("\\..*", "", v)
#[1] "7" "8" "12" "11"
or a few stringi options:
library(stringi)
stri_replace_first_regex(v, "\\..*", "")
#[1] "7" "8" "12" "11"
# extract vs. replace
stri_extract_first_regex(v, "[^\\.]+")
#[1] "7" "8" "12" "11"
If you want to use a splitting approach, these will work:
unlist(strsplit(v, "\\..*"))
#[1] "7" "8" "12" "11"
# stringi option
unlist(stri_split_regex(v, "\\..*", omit_empty=TRUE))
#[1] "7" "8" "12" "11"
unlist(stri_split_fixed(v, ".", n=1, tokens_only=TRUE))
unlist(stri_split_regex(v, "[^\\w]", n=1, tokens_only=TRUE))
Other sub variations that use a capture group to target the leading characters specifically:
sub("(\\w+).+", "\\1", v) # \w matches [[:alnum:]_] (i.e. alphanumerics and underscores)
sub("([[:alnum:]]+).+", "\\1", v) # exclude underscores
# variations on a theme
sub("(\\w+)\\..*", "\\1", v)
sub("(\\d+)\\..*", "\\1", v) # narrower: \d for digits specifically
sub("(.+)\\..*", "\\1", v) # broader: "." matches any single character
# stringi variation just for fun:
stri_extract_first_regex(v, "\\w+")
scan() would actually work well for this. Since we want everything before the first ., we can use that as a comment character and scan() will remove everything after and including that character, for each element in v.
scan(text = v, comment.char = ".")
# [1] 7 8 12 11
The above returns a numeric vector, which might be where you are headed. If you need to stick with characters, add the what argument to denote we want a character vector returned.
scan(text = v, comment.char = ".", what = "")
# [1] "7" "8" "12" "11"
Data:
v <- c("7.7.4", "8", "12.6", "11.5.2.1")
toString seems to convert a whole vector to a single string -
toString(c(1,2))
[1] "1, 2"
how does one map the string conversion over each element; i.e. for the above example, to obtain ("1", "2") ?
> as.character(c(1,2))
[1] "1" "2"
Is the output I get from the R-console.
Since the result is a character vector with a single element, the strategy of using as.character will have no effect. Need to use scan:
> scan(text = toString(0:11), sep="," )
Read 12 items
[1] 0 1 2 3 4 5 6 7 8 9 10 11
Then you can use as.character if that is needed:
> res <- scan(text = toString(0:11), sep="," )
Read 12 items
> as.character(res)
[1] "0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11"
I prefer paste0 since it's shorter and (from what I can tell) accomplishes the same thing as as.character:
> paste0(1:2)
[1] "1" "2"
> identical(paste0(1:2),as.character(1:2))
[1] TRUE
> test = "23*45"
I'd like to split testby the symbol *
I tried...
> strsplit(test,'*')
and I got...
[[1]]
[1] "2" "3" "*" "4" "5"
What I aim to have is:
[[1]]
[1] "23" "45"
You need to escape the star...
test = "23*45"
strsplit( test , "\\*" )
#[[1]]
#[1] "23" "45"
The split is a regular expression and * means the preceeding item is matched zero or more times. You are splitting on nothing , i.e. splitting into individual characters, as noted in the Details section of strsplit(). \\* means *treat * as a literal *.
Alternatively use the fixed argument...
strsplit( test , "*" , fixed = TRUE )
#[[1]]
#[1] "23" "45"
Which gets R to treat the split pattern as literal and not a regular expression.
You might want to look at this package:
http://www.rexamine.com/resources/stringi/
To install this package simply run:
install.packages("stringi")
Example:
stri_split_fixed(test, "*")
Obviously I dont get the way grep works in R. If I use grep on my OS X terminal, I am able to use the parameter -o which makes grep only return the matching part. In R, I can't find how to do a corresponding thing. Reading the manual I thought values was the right approach, which is better inasmuch that it returns characters not indexes, but still returns the whole string.
# some string fasdjlk465öfsdj123
# R
test <- fasdjlk465öfsdj123
grep("[0-9]",test,value=TRUE) # returns "fasdjlk465öfsdj123"
# shell
grep -o '[0-9]' fasdjlk465öfsdj123
# returns 4 6 5 1 2 3
What's the parameter I am missing in R ?
EDIT: Joris Meys' suggestions comes really close to what I am trying to do. I get a vector as a result of readLines. And I'd like to check every element of the vector for numbers and return these numbers. I am really surprised there's no standard solution for that. I thought of using some regexp function that works on a string and returns the match like grep -o and then use lapply on that vector. grep.custom comes closest – i'll try to make that work for me.
Spacedman said it already. If you really want to simulate grep in the shell, you have to work on the characters itself, using strsplit() :
> chartest <- unlist(strsplit(test,""))
> chartest
[1] "f" "a" "s" "d" "j" "l" "k" "4" "6" "5" "ö" "f" "s" "d" "j" "1" "2" "3"
> grep("[0-9]",chartest,value=T)
[1] "4" "6" "5" "1" "2" "3"
EDIT :
As Nico said, if you want to do this for complete regular expressions, you need to use the gregexpr() and substr(). I'd make a custom function like this one :
grep.custom <- function(x,pattern){
strt <- gregexpr(pattern,x)[[1]]
lngth <- attributes(strt)$match.length
stp <- strt + lngth - 1
apply(cbind(strt,stp),1,function(i){substr(x,i[1],i[2])})
}
Then :
> grep.custom(test,"sd")
[1] "sd" "sd"
> grep.custom(test,"[0-9]")
[1] "4" "6" "5" "1" "2" "3"
> grep.custom(test,"[a-z]s[a-z]")
[1] "asd" "fsd"
EDIT2 :
for vectors, use the function Vectorize(), eg:
> X <- c("sq25dfgj","sqd265jfm","qs55d26fjm" )
> v.grep.custom <- Vectorize(grep.custom)
> v.grep.custom(X,"[0-9]+")
$sq25dfgj
[1] "25"
$sqd265jfm
[1] "265"
$qs55d26fjm
[1] "55" "26"
and if you want to call grep from the shell, see ?system
That's because 'grep' for R works on vectors - it will do the search on every element and return the element indices that match. It says 'which elements in this vector match this pattern?' For example, here we make a vector of 3 and then ask 'which elements in this vector have a single number in them?'
> test = c("fasdjlk465öfsdj123","nonumbers","123")
> grep("[0-9]",test)
[1] 1 3
Elements 1 and 3 - not 2, which is only characters.
You probably want gsub - substitute anything that doesn't match digits with nothing:
> gsub("[^0-9]","",test)
[1] "465123" "" "123"
All this dancing around with strings is the problem the stringr package was designed to solve.
library(stringr)
str_extract_all('fasdjlk465fsdj123', '[0-9]')
[[1]]
[1] "4" "6" "5" "1" "2" "3"
# It is vectorized too
str_extract_all(rep('fasdjlk465fsdj123',3), '[0-9]')
[[1]]
[1] "4" "6" "5" "1" "2" "3"
[[2]]
[1] "4" "6" "5" "1" "2" "3"
[[3]]
[1] "4" "6" "5" "1" "2" "3"
The motivation behind stringr is to unify string operations in R under two principles:
Use a sane and consistent naming scheme for functions (str_do_something).
Make it so that all the string operations that take one step in other programing languages, yet fifty steps in R, take only one step in R.
grep will only tell you whether the string matches or not.
For instance if you have:
values <- c("abcde", "12345", "abc123", "123abc")
Then
grep <- ("[0-9]", values)
[1] 2 3 4
This tells you that elements 2,3 and 4 of the array match the regexp. You can pass value=TRUE to return the strings rather then the indices.
If you want to check where the match is happening you can use regexpr instead
> regexpr("[0-9]", values)
[1] -1 1 4 1
attr(,"match.length")
[1] -1 1 1 1
which tells you where the first match is happening.
Even better, you can use gregexpr for multiple matches
> gregexpr("[0-9]", values)
[[1]]
[1] -1
attr(,"match.length")
[1] -1
[[2]]
[1] 1 2 3 4 5
attr(,"match.length")
[1] 1 1 1 1 1
[[3]]
[1] 4 5 6
attr(,"match.length")
[1] 1 1 1
[[4]]
[1] 1 2 3
attr(,"match.length")
[1] 1 1 1
No idea where you get the impression that
> test <- "fasdjlk465öfsdj123"
> grep("[0-9]",test)
[1] 1
returns "fasdjlk465öfsdj123"
If you want to return the matches, you need to break test into it's component parts, grep on those and then use the thing returned from grep to index test.
> test <- strsplit("fasdjlk465öfsdj123", "")[[1]]
> matched <- grep("[0-9]", test)
> test[matched]
[1] "4" "6" "5" "1" "2" "3"
Or just return the matched strings directly, depends what you want:
> grep("[0-9]", test, value = TRUE)
[1] "4" "6" "5" "1" "2" "3"
strapply in the gsubfn package can do such extraction:
> library(gsubfn)
> strapply(c("ab34de123", "55x65"), "\\d+", as.numeric, simplify = TRUE)
[,1] [,2]
[1,] 34 55
[2,] 123 65
Its based on the apply paradigm where the first argument is the object, the second is the modifier (margin for apply, regular expression for strapply) and the third argument is the function to apply on the matches.
str_extract_all(obj, re) in the stringr package is similar to strapply specialized to use c for the function, i.e. its the similar to strapply(obj, re, c) .
strapply supports the sets of regular expressions supported by R and also supports tcl regular expressions.
See the gsubfn home page at http://gsubfn.googlecode.com