Remove any characters before "_"

Question

How can I remove any characters and digits before "_"; as an example:

> char <- c("SRR04_d3_GCTCGGTAAGCACCTCGCCACATA","SRR04_d1_ACTCGGTAAGCACCTCGCCACATA",
+           "JH-HL_GCTCGGTAAGCATGTCGCCACATA","HZ04_d5_GCTCGGTAAGCACCTCGCCACATA")
> c("GCTCGGTAAGCACCTCGCCACATA","ACTCGGTAAGCACCTCGCCACATA",
+           "GCTCGGTAAGCATGTCGCCACATA","GCTCGGTAAGCACCTCGCCACATA")
[1] "GCTCGGTAAGCACCTCGCCACATA" "ACTCGGTAAGCACCTCGCCACATA" "GCTCGGTAAGCATGTCGCCACATA"
[4] "GCTCGGTAAGCACCTCGCCACATA"

Can I do this with str_replace function from tidyverse

score 2 · Accepted Answer · answered Oct 10 '21 at 07:03

2

You may do this with sub -

sub('.*_', '', char)

#[1] "GCTCGGTAAGCACCTCGCCACATA" "ACTCGGTAAGCACCTCGCCACATA"
#[3] "GCTCGGTAAGCATGTCGCCACATA" "GCTCGGTAAGCACCTCGCCACATA"

Or if you prefer stringr functions.

stringr::str_remove(char, '.*_')
stringr::str_replace(char, '.*_', '')

answered Oct 10 '21 at 07:03

Ronak Shah

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1

This removes the _ I'm not 100% sure the OP wanted that. He said before. If he doesn't then the '' in sub or str_replace can be '_'. In the sample data there is a string of the form "sometext_moretext_lasttext" what does the OP want as the result? moretext_lasttext or just lasttext - check you get what you want/expect – CALUM Polwart Oct 10 '21 at 07:11

score 2 · Answer 2 · answered Oct 10 '21 at 07:17

2

Base R:

Or use strsplit and sapply:

> sapply(strsplit(char, '_'), tail, n=1)
[1] "GCTCGGTAAGCACCTCGCCACATA" "ACTCGGTAAGCACCTCGCCACATA" "GCTCGGTAAGCATGTCGCCACATA" "GCTCGGTAAGCACCTCGCCACATA"
>

answered Oct 10 '21 at 07:17

U13-Forward

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score 2 · Answer 3 · answered Oct 10 '21 at 07:18

2

Here is an alternative way:

library(stringr)
str_replace_all(char, ".*_(?=[^:]+$)", "")

output:

[1] "GCTCGGTAAGCACCTCGCCACATA" "ACTCGGTAAGCACCTCGCCACATA" "GCTCGGTAAGCATGTCGCCACATA"
[4] "GCTCGGTAAGCACCTCGCCACATA"

answered Oct 10 '21 at 07:18

TarJae

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score 2 · Answer 4 · answered Oct 10 '21 at 18:16

2

We may use trimws from base R

trimws(char, whitespace = ".*_")
[1] "GCTCGGTAAGCACCTCGCCACATA" "ACTCGGTAAGCACCTCGCCACATA" 
[3] "GCTCGGTAAGCATGTCGCCACATA" "GCTCGGTAAGCACCTCGCCACATA"

answered Oct 10 '21 at 18:16

akrun

874,273
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score 1 · Answer 5 · answered Oct 10 '21 at 07:11

The package stringr can be used to extract all the letters at the end of the string with:

library(stringr)
str_extract(char, "[[:alpha:]]*$")
# [1] "GCTCGGTAAGCACCTCGCCACATA" "ACTCGGTAAGCACCTCGCCACATA" "GCTCGGTAAGCATGTCGCCACATA"
# [4] "GCTCGGTAAGCACCTCGCCACATA"

score 1 · Answer 6 · answered Oct 10 '21 at 07:16

I would phrase your problem using gsub with the pattern [^\W_]+_. This will target one or more alphanumeric characters before an underscore, any number of times.

char <- c("SRR04_d3_GCTCGGTAAGCACCTCGCCACATA","SRR04_d1_ACTCGGTAAGCACCTCGCCACATA",
      "JH-HL_GCTCGGTAAGCATGTCGCCACATA","HZ04_d5_GCTCGGTAAGCACCTCGCCACATA")
output <- gsub("[^\\W_]+_", "", char)
output

[1] "GCTCGGTAAGCACCTCGCCACATA" "ACTCGGTAAGCACCTCGCCACATA"
[3] "GCTCGGTAAGCATGTCGCCACATA" "GCTCGGTAAGCACCTCGCCACATA"

Remove any characters before "_"

6 Answers6