How to extract substring from a string up to a certain occurrence of a character

Question

How to extract substring from a string up to a certain occurrence of a character.

For example:

string <- 'test_file_csv_name.csv'

Up to the second occurrence of _

Expected output:

'test_file'

Try `sub("([^_]*_[^_]*)_.*", "\\1", string)` – GKi Jun 16 '20 at 12:28 — GKi, Jun 16 '20 at 12:28

score 2 · Accepted Answer · answered Jun 16 '20 at 12:29

2

Using sub, we can capture the portion of the file name you want, removing the rest:

string <- 'test_file_csv_name.csv'
sub("^([^_]+_[^_]+).*$", "\\1", string)

[1] "test_file"

answered Jun 16 '20 at 12:29

Tim Biegeleisen

score 1 · Answer 2 · answered Jun 16 '20 at 12:29

1

are you asking to keep a certain amout of _

you can use

sub("((.*?_){1}.*?)_.*","\\1",string)

change {1} to keep the amount of _ you'd like

answered Jun 16 '20 at 12:29

Daniel O

score 1 · Answer 3 · answered Jun 16 '20 at 12:39

1

Beside using sub (e.g. sub("([^_]*_[^_]*).*", "\\1", string)) you can use substr using the position found by gregexpr:

substr(string, 1, gregexpr("_", string)[[1]][2]-1)
#[1] "test_file"

answered Jun 16 '20 at 12:39

GKi

3 Answers3