I have a data frame with column names z_1, z_2 upto z_200. In the following example, for ease of representation, I am showing only z_1
df <- data.frame(x=1:5, y=2:6, z_1=3:7, u=4:8)
df
i=1
tmp <- paste("z",i,sep="_")
subset(df, select=-c(tmp))
The above code will be used in a loop i for accessing certain elements that need to be removed from the data frame
While executing the above code, I get the error "Error in -c(tmp) : invalid argument to unary operator"
Thank you for your help
Try:
df[names(df)!=tmp]
The reason your code is not working is because -c(tmp), where tmp is a character, evaluates to nothing. You can use this way of excluding with numerical values only.
Alternatively this would also work:
subset(df, select=-which(names(df)==tmp))
Because which returns a number.
I you want to use subset and have a large number of columns of similar names to include or exclude, I usually think about using grepl to construct a logical vector of matches to column names (or you could use it to construct a numeric vector just as easily). Negation of the result would remove columns
df <- data.frame(x=1:5, y=2:6, z_1=3:7, u=4:8)
df
i=1
tmp <- paste("z",i,sep="_")
subset(df, select= !grepl("^z", names(df) ) )
x y u
1 1 2 4
2 2 3 5
3 3 4 6
4 4 5 7
5 5 6 8
With negation this lets you remove (or without it include) all of the columns starting with "z" using that pattern. Or you can use grep with value =TRUE in combination with character values:
subset(df, select= c("x", grep("^z", names(df), value=TRUE ) ) )
Related
I have a script generating a dataframe with multiple columns named with numbers 1, 2, 3 –> n
I want to rename the columns with the following names: "Cluster_1", "Cluster_2", "Cluster_3" –> "Cluster_n" (with incrementation).
As the number of columns in my dataframe can change accordingly to another part of my script, I would like to be able to have a kind of loop structure that would go through my dataframe and change columns accordingly.
I would like to do something like:
for (i in colnames(df)){
an expression that would change the column name to a concatenation of "Cluster_" + i
}
Outside the loop context, I generally use this expression to rename a column:
names(df)[names(df) == '1'] <- 'Cluster_1'
But I struggle to produce an adapted version of this expression that would properly integrate in my for loop with a concatenation of string and variable value.
How can I adjust the expression that renames the column of the dataframe to integrate in my for loop?
Or is there a better way than a for loop to do this?
A tidyverse solution: rename_with()
require(dplyr)
## '~' notation can be used for formulae in this context:
df <- rename_with(df, ~ paste0("Cluster_", .))
Using paste0.
names(df) <- paste0('cluster_', seq_len(length(df)))
If you really need a for loop, try
for (i in seq_along(names(df))) {
names(df)[i] <- paste0('cluster_', i)
}
df
# cluster_1 cluster_2 cluster_3 cluster_4
# 1 1 4 7 10
# 2 2 5 8 11
# 3 3 6 9 12
Note: colnames()/rownames() is designed for class "matrix", for "data.frame"s, you might want to use names()/row.names().
Data:
df <- data.frame(matrix(1:12, 3, 4))
I'm working with multiple big data frames in R and I'm trying to write functions that can modify each of them (given a set of common parameters). One function is giving me trouble (shown below).
RawData <- function(x)
{
for(i in 1:nrow(x))
{
if(grep(".DERIVED", x[i,]) >= 1)
{
x <- x[-i,]
}
}
for(i in 1:ncol(x))
{
if(is.numeric(x[,i]) != TRUE)
{
x <- x[,-i]
}
}
return(x)
}
The objective of this function is twofold: first, to remove any rows that contain a ".DERIVED" string in any one of their cells (using grep), and second, to remove any columns that are non-numeric (using is.numeric). I get an error on the following condition:
if(grep(".DERIVED", x[i,]) >= 1)
The error states the "argument is of zero length", which I believe is usually associated with NULL values in a vector. However, I've used is.null on the entire data frame that is giving me errors, and it confirmed that there are no null values in the DF. I'm sure I'm missing something relatively simple here. Any advice would be greatly appreciated.
If you can use non-base-R functions, this should address your issue. df is the data.frame in question here. It will also be faster than looping over rows (generally not advised if avoidable).
library(dplyr)
library(stringr)
df %>%
filter_all(!str_detect(., '\\.DERIVED')) %>%
select_if(is.numeric)
You can make it a function just as you would anything else:
mattsFunction <- function(dat){
dat %>%
filter_all(!str_detect(., '\\.DERIVED')) %>%
select_if(is.numeric)
}
you should probably give it a better name though
The error is from the line
if(grep(".DERIVED", x[i,]) >= 1)
When grep doesn't find the term ".DERIVED", it returns something of zero length, your inequality doesn't return TRUE or FALSE, but rather returns logical(0). The error is telling you that the if statement cannot evaluate whether logical(0) >= 1
A simple example:
if(grep(".DERIVED", "1234.DERIVEDabcdefg") >= 1) {print("it works")} # Works nicely, since the inequality can be evaluated
if(grep(".DERIVED", "1234abcdefg") > 1) {print("no dice")}
You can replace that line with if(length(grep(".DERIVED", x[i,])) != 0)
There's something else you haven't noticed yet, which is that you're removing rows/columns in a loop. Say you remove the 5th column, the next loop iteration (when i = 6) will be handling what was the 7th row! (this will end in an error along the lines of Error in[.data.frame(x, , i) : undefined columns selected)
I prefer using dplyr, but if you need to use base R functions there are ways to to this without if statements.
Notice that you should consider using the regex version of "\\.DERIVED" and not ".DERIVED" which would mean "any character followed by DERIVED".
I don't have example data or output, so here's my best go...
# Made up data
test <- data.frame(a = c("data","data.DERIVED","data","data","data.DERIVED"),
b = (c(1,2,3,4,5)),
c = c("A","B","C","D","E"),
d = c(2,5,6,8,9),
stringsAsFactors = FALSE)
# Note: The following code assumes that the column class is numeric because the
# example code provided assumed that the column class was numeric. This will not
# detects if the column is full of a string of character values of only numbers.
# Using the base subset command
test2 <- subset(test,
subset = !grepl("\\.DERIVED",test$a),
select = sapply(test,is.numeric))
# > test2
# b d
# 1 1 2
# 3 3 6
# 4 4 8
# Trying to use []. Note: If only 1 column is numeric this will return a vector
# instead of a data.frame
test2 <- test[!grepl("\\.DERIVED",test$a),]
test2 <- test2[,sapply(test,is.numeric)]
# > test2
# b d
# 1 1 2
# 3 3 6
# 4 4 8
I am trying to train a data that's converted from a document term matrix to a dataframe. There are separate fields for the positive and negative comments, so I wanted to add a string to the column names to serve as a "tag", to differentiate the same word coming from the different fields - for example, the word hello can appear both in the positive and negative comment fields (and thus, represented as a column in my dataframe), so in my model, I want to differentiate these by making the column names positive_hello and negative_hello.
I am looking for a way to rename columns in such a way that a specific string will be appended to all columns in the dataframe. Say, for mtcars, I want to rename all of the columns to have "_sample" at the end, so that the column names would become mpg_sample, cyl_sample, disp_sample and so on, which were originally mpg, cyl, and disp.
I'm considering using sapplyor lapply, but I haven't had any progress on it. Any help would be greatly appreciated.
Use colnames and paste0 functions:
df = data.frame(x = 1:2, y = 2:1)
colnames(df)
[1] "x" "y"
colnames(df) <- paste0('tag_', colnames(df))
colnames(df)
[1] "tag_x" "tag_y"
If you want to prefix each item in a column with a string, you can use paste():
# Generate sample data
df <- data.frame(good=letters, bad=LETTERS)
# Use the paste() function to append the same word to each item in a column
df$good2 <- paste('positive', df$good, sep='_')
df$bad2 <- paste('negative', df$bad, sep='_')
# Look at the results
head(df)
good bad good2 bad2
1 a A positive_a negative_A
2 b B positive_b negative_B
3 c C positive_c negative_C
4 d D positive_d negative_D
5 e E positive_e negative_E
6 f F positive_f negative_F
Edit:
Looks like I misunderstood the question. But you can rename columns in a similar way:
colnames(df) <- paste(colnames(df), 'sample', sep='_')
colnames(df)
[1] "good_sample" "bad_sample" "good2_sample" "bad2_sample"
Or to rename one specific column (column one, in this case):
colnames(df)[1] <- paste('prefix', colnames(df)[1], sep='_')
colnames(df)
[1] "prefix_good_sample" "bad_sample" "good2_sample" "bad2_sample"
You can use setnames from the data.table package, it doesn't create any copy of your data.
library(data.table)
df <- data.frame(a=c(1,2),b=c(3,4))
# a b
# 1 1 3
# 2 2 4
setnames(df,paste0(names(df),"_tag"))
print(df)
# a_tag b_tag
# 1 1 3
# 2 2 4
for a dataframe df, I need to find the unique values for some_col. Tried the following
length(unique(df["some_col"]))
but this is not giving the expected results. However length(unique(some_vector)) works on a vector and gives the expected results.
Some preceding steps while the df is created
df <- read.csv(file, header=T)
typeof(df) #=> "list"
typeof(unique(df["some_col"])) #=> "list"
length(unique(df["some_col"])) #=> 1
Try with [[ instead of [. [ returns a list (a data.frame in fact), [[ returns a vector.
df <- data.frame( some_col = c(1,2,3,4),
another_col = c(4,5,6,7) )
length(unique(df[["some_col"]]))
#[1] 4
class( df[["some_col"]] )
[1] "numeric"
class( df["some_col"] )
[1] "data.frame"
You're getting a value of 1 because the list is of length 1 (1 column), even though that 1 element contains several values.
you need to use
length(unique(unlist(df[c("some_col")])))
When you call column by df[c("some_col")] or by df["some_col"] ; it pulls it as a list. Unlist will convert it into the vector and you can work easily with it. When you call column by df$some_col .. it pulls the data column as vector
I think you might just be missing a ,
Try
length(unique(df[,"some_col"]))
In response to comment :
df <- data.frame(cbind(A=c(1:10),B=rep(c("A","B"),5)))
df["B"]
Output :
B
1 A
2 B
3 A
4 B
5 A
6 B
7 A
8 B
9 A
10 B
and
length(unique(df[,"B"]))
Output:
[1] 1
Which is the same incorrect/undesirable output as the OP posted
HOWEVER With a comma ,
df[,"B"]
Output :
[1] A B A B A B A B A B
Levels: A B
and
length(unique(df[,"B"]))
Now gives you the correct/desired output by the OP. Which in this example is 2
[1] 2
The reason is that df["some_col"] calls a data.frame and length call to an object class data.frame counts the number of data.frames in that object which is 1, while df[,"some_col"] returns a vector and length call to a vector correctly returns the number of elements in that vector. So you see a comma (,) makes all the difference.
using tidyverse
df %>%
select("some_col") %>%
n_distinct()
The data.table package contains the convenient shorthand uniqueN. From the documentation
uniqueN is equivalent to length(unique(x)) when x is anatomic vector, and nrow(unique(x)) when x is a data.frame or data.table. The number of unique rows are computed directly without materialising the intermediate unique data.table and is therefore faster and memory efficient.
You can use it with a data frame:
df <- data.frame(some_col = c(1,2,3,4),
another_col = c(4,5,6,7) )
data.table::uniqueN(df[['some_col']])
[1] 4
or if you already have a data.table
dt <- setDT(df)
dt[,uniqueN(some_col)]
[1] 4
Here is another option:
df %>%
distinct(column_name) %>%
count()
or this without tidyverse:
count(distinct(df, column_name))
checking benchmarks in the web you will see that distinct() is fast.
In my code, I am filling the columns of a dataframe with vectors, as so:
df1[columnNum] <- barWidth
This works fine, except for one thing: I want the name of the vector variable (barWidth above) to be retained as the column header, one column at a time. Furthermore, I do not wish to use cbind. This slows the execution of my code down considerably. Consequently, I am using a pre-allocated dataframe.
Can this be done in the vector-to-column assignment? If not, then how do I change it after the fact? I can't find the right syntax to do this with colNames().
TIA
It's being done by the [<-.data.frame function. It could conceivably be replaced by one that looked at the name of the argument but it's such a fundamental function I would be hesitant. Furthermore there appears to be an aversion to that practice signaled by this code at the top of the function definition:
> `[<-.data.frame`
function (x, i, j, value)
{
if (!all(names(sys.call()) %in% c("", "value")))
warning("named arguments are discouraged")
nA <- nargs()
if (nA == 4L) {
<snipped rest of rather long definition>
I don't know why that is there, but it is. Maybe you should either be thinking about using names<- after the column assignment, or using this method:
> dfrm["barWidth"] <- barWidth
> dfrm
a V2 barWidth
1 a 1 1
2 b 2 2
3 c 3 3
4 d 4 4
This can be generalized to a list of new columns:
dfrm <- data.frame(a=letters[1:4])
barWidth <- 1:4
newcols <- list(barWidth=barWidth, bw2 =barWidth)
dfrm[names(newcol)] <- newcol
dfrm
#
a barWidth bw2
1 a 1 1
2 b 2 2
3 c 3 3
4 d 4 4
If you have the list of names of vectors you want to apply you could do:
namevec <- c(...,"barWidth"...,)
columnNums <- c(...,10,...)
df1[columnNums[i]] <- get(namevec[i])
names(df1)[columnNums[i]] <- namevec[i]
or even
columnNums <- c(barWidth=4,...)
for (i in seq_along(columnNums)) {
df1[columnNums[i]] <- get(names(columnNums)[i])
}
names(df1)[columnNums] <- names(columnNums)
but the deeper question would be where this set of vectors is coming from in the first place: could you have them in a list all along?
I'd simply use cbind():
df1 <- cbind( df1, barWidth )
which retains the name. It will, however, end up as the last column in df1