This turns out to be quite easy...
Given:
> head(data)
inst a1 a2 a3 a4 a5 a6 a7 a8 escore
1 1 1 1 0 1 1 0 0 0 4
2 1 0 1 0 0 0 0 0 0 1
3 1 1 0 0 1 0 1 1 1 2
4 1 0 1 0 0 0 1 0 0 1
You can use grep on the names of the columns in data
> # returns the column numbers of cols that begin with "a"
> grep("^a", names(data))
[1] 2 3 4 5 6 7 8 9
> data[,grep("^a", names(data))]
a1 a2 a3 a4 a5 a6 a7 a8
1 1 1 0 1 1 0 0 0
2 0 1 0 0 0 0 0 0
3 1 0 0 1 0 1 1 1
4 0 1 0 0 0 1 0 0
5 0 0 0 0 0 1 0 0
and, of course, you can use any regular expression you like.
-Wil
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