CODEWITHSUNDEEP
rregexstring
Lisann
Lisann

Reputation: 5855

Remove part of a string

How do I remove part of a string? For example in ATGAS_1121 I want to remove everything before _.

Upvotes: 114

Views: 343084

Answers (6)

Agile Bean
Agile Bean

Reputation: 7151

Maybe the most intuitive solution is probably to use the stringr function str_remove which is even easier than str_replace as it has only 1 argument instead of 2.

The only tricky part in your example is that you want to keep the underscore but its possible: You must match the regular expression until it finds the specified string pattern (?=pattern).

See example:

strings = c("TGAS_1121", "MGAS_1432", "ATGAS_1121")
strings %>% stringr::str_remove(".+?(?=_)")

[1] "_1121" "_1432" "_1121"

Upvotes: 9

naught101
naught101

Reputation: 19543

If you're a Tidyverse kind of person, here's the stringr solution:

R> library(stringr)
R> strings = c("TGAS_1121", "MGAS_1432", "ATGAS_1121") 
R> strings %>% str_replace(".*_", "_")
[1] "_1121" "_1432" "_1121"
# Or:
R> strings %>% str_replace("^[A-Z]*", "")
[1] "_1121" "_1432" "_1121"

Upvotes: 34

KK_63
KK_63

Reputation: 105

Here the strsplit solution for a dataframe using dplyr package

col1 = c("TGAS_1121", "MGAS_1432", "ATGAS_1121") 
col2 = c("T", "M", "A") 
df = data.frame(col1, col2)
df
        col1 col2
1  TGAS_1121    T
2  MGAS_1432    M
3 ATGAS_1121    A

df<-mutate(df,col1=as.character(col1))
df2<-mutate(df,col1=sapply(strsplit(df$col1, split='_', fixed=TRUE),function(x) (x[2])))
df2

  col1 col2
1 1121    T
2 1432    M
3 1121    A

Upvotes: 4

verbamour
verbamour

Reputation: 985

Here's the strsplit solution if s is a vector:

> s <- c("TGAS_1121", "MGAS_1432")
> s1 <- sapply(strsplit(s, split='_', fixed=TRUE), function(x) (x[2]))
> s1
[1] "1121" "1432"

Upvotes: 25

Joshua Ulrich
Joshua Ulrich

Reputation: 176648

Use regular expressions. In this case, you can use gsub:

gsub("^.*?_","_","ATGAS_1121")
[1] "_1121"

This regular expression matches the beginning of the string (^), any character (.) repeated zero or more times (*), and underscore (_). The ? makes the match "lazy" so that it only matches are far as the first underscore. That match is replaced with just an underscore. See ?regex for more details and references

Upvotes: 154

doug
doug

Reputation: 70038

You can use a built-in for this, strsplit:

> s = "TGAS_1121"
> s1 = unlist(strsplit(s, split='_', fixed=TRUE))[2]
> s1    
 [1] "1121"

strsplit returns both pieces of the string parsed on the split parameter as a list. That's probably not what you want, so wrap the call in unlist, then index that array so that only the second of the two elements in the vector are returned.

Finally, the fixed parameter should be set to TRUE to indicate that the split parameter is not a regular expression, but a literal matching character.

Upvotes: 47

Related Questions