
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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