Using grep to filter rows with two or more patterns in the string in R

Question

I need to index all the rows that have a string beginning with either "B-" or "B^" in one of the columns. I tried a bunch of combinations, but I am suspecting it might not be working due to "-" and "^" signs being part of grep command as well.

dataset[grep('^(B-|B^)[^B-|B^]*$', dataset$Col1),]

With the above script, rows beginning with "B^" are not being extracted. Please suggest a smart way to handle this.

Dave Gruenewald · Accepted Answer · 2019-03-18 18:27:07Z

1

You can use the escape \\ command in grep:

dataset[grep('^(B\\-|B\\^)[^B\\-|B\\^]*$', dataset$Col1),]

answered Mar 18, 2019 at 18:27

Dave Gruenewald

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Yleduap Over a year ago

That worked perfectly. Thank you!! And thanks for inline edits too :)

Chthonyx · Accepted Answer · 2019-03-18 22:11:14Z

0

For further explanation, the ^ matches the beginning of a string as an anchor therefore you have to escape it in the middle of string. The [] are a character class so [^B-|B^]* matches any character that's not a B,-,B, or ^. They are unnecessary here.

The simplified regex is: dataset[grep('^(B-|B\\^)', dataset$Col1),]

answered Mar 18, 2019 at 22:11

Chthonyx

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1 Comment

Yleduap Over a year ago

I see your point about not needing the [ ] character class. Thank you for the insight!

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