Ben Ben - 1 year ago 71
R Question

How to extract everything until first occurrence of pattern

I'm trying to use the stringr package in R to extract everything from a string up until the first occurrence of an underscore.

What I've tried

str_extract("L0_123_abc", ".+?(?<=_)")
> "L0_"

Close but no cigar. How do I get this one? Also, Ideally I'd like something that's easy to extend so that I can get the information in between the 1st and 2nd underscore and get the information after the 3rd underscore.

Answer Source

To get L0, you may use

> library(stringr)
> str_extract("L0_123_abc", "[^_]+")
[1] "L0"

The [^_]+ matches 1 or more chars other than _.

Also, you may split the string with _:

x <- str_split("L0_123_abc", fixed("_"))
> x
[1] "L0"  "123" "abc"

This way, you will have all the substrings you need.

The same can be achieved with

> str_extract_all("L0_123_abc", "[^_]+")
[1] "L0"  "123" "abc"
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