How to select R data.table rows based on substring match (a la SQL like)

Question

I have a data.table with a character column, and want to select only those rows that contain a substring in it. Equivalent to SQL WHERE x LIKE \'%substring%\'<

Answer 1

data.table has a like function.

Months[like(Name,"mb")]
        Name Number
1: September      9
2:  November     11
3:  December     12

Or, %like% looks nicer :

> Months[Name %like% "mb"]
    Name Number
1: September      9
2:  November     11
3:  December     12

Note that %like% and like() use grepl (returns logical vector) rather than grep (returns integer locations). That's so it can be combined with other logical conditions :

> Months[Number<12 & Name %like% "mb"]
        Name Number
1: September      9
2:  November     11

and you get the power of regular expression search (not just % or * wildcard), too.