CODEWITHSUNDEEP
stringr
Lisa Ann
Lisa Ann

Reputation: 3485

Extract the first (or last) n characters of a string

I want to extract the first (or last) n characters of a string. This would be the equivalent to Excel's LEFT() and RIGHT(). A small example:

# create a string
a <- paste('left', 'right', sep = '')
a
# [1] "leftright"

I would like to produce b, a string which is equal to the first 4 letters of a:

b
# [1] "left"

What should I do?

Upvotes: 125

Views: 264878

Answers (5)

gbganalyst
gbganalyst

Reputation: 384

For those coming from Microsoft Excel or Google Sheets, you would have seen functions like LEFT(), RIGHT(), and MID(). I have created a package known as forstringr and its development version is currently on Github.

if(!require("devtools")){
 install.packages("devtools")
}

devtools::install_github("gbganalyst/forstringr")

library(forstringr)

  • the str_left(): This counts from the left and then extract n characters

  • the str_right()- This counts from the right and then extract n characters

  • the str_mid()- This extract characters from the middle

Examples:


x <- "some text in a string"

str_left(x, 4)

[1] "some"

str_right(x, 6)

[1] "string"

str_mid(x, 6, 4)

[1] "text"

Upvotes: 8

Andrea Cirillo
Andrea Cirillo

Reputation: 594

You can easily obtain Right() and Left() functions starting from the Rbase package:

  • right function

    right = function (string, char) {
    substr(string,nchar(string)-(char-1),nchar(string))
}

  • left function

    left = function (string,char) {
    substr(string,1,char)
}

you can use those two custom-functions exactly as left() and right() in excel. Hope you will find it useful

Upvotes: 34

Marcos RF
Marcos RF

Reputation: 337

Make it simple and use R basic functions:

# To get the LEFT part:
> substr(a, 1, 4)
[1] "left"
> 
# To get the MIDDLE part:
> substr(a, 3, 7)
[1] "ftrig"
> 
# To get the RIGHT part:
> substr(a, 5, 10)
[1] "right"

The substr() function tells you where start and stop substr(x, start, stop)

Upvotes: 9

juba
juba

Reputation: 49073

The stringr package provides the str_sub function, which is a bit easier to use than substr, especially if you want to extract right portions of your string :

R> str_sub("leftright",1,4)
[1] "left"
R> str_sub("leftright",-5,-1)
[1] "right"

Upvotes: 94

rcs
rcs

Reputation: 68849

See ?substr

R> substr(a, 1, 4)
[1] "left"

Upvotes: 118

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