Re: [R] Select subset of data

From: David Winsemius <dwinsemius_at_comcast.net>
Date: Tue, 29 Mar 2011 16:36:35 -0400

On Mar 29, 2011, at 3:40 PM, Lisa wrote:

> Dear All,
>
> I have a dataset that looks like this:
>
> group subject result v4 v5
> 1 1 1 0 1 0
> 2 1 2 1 0 0
> 3 1 3 0 0 0
> 4 1 4 1 0 0
> 5 2 1 0 1 1
> 6 2 2 0 0 1
> 7 2 3 0 1 1
> 8 3 1 0 1 0
> 9 3 2 0 0 1
> 10 3 3 1 0 0
> 11 3 4 0 1 0
> 12 4 1 1 0 0
> 13 4 2 1 1 0
> 14 4 3 0 0 1
> 15 4 4 0 0 0
> 16 4 5 1 0 1
>
>
> I only show 4 groups here. There are several subjects within each
> group. I
> want to select some groups in which for the firs two subjects, the
> results
> are equal to 0, and for the other subjects, only one has the result
> being
> equal to 1. So, for the data above, only the group 3 satisfies these
> conditions. Therefore, the new dataset is:
>
> group subject result v4 v5
> 8 3 1 0 1 0
> 9 3 2 0 0 1
> 10 3 3 1 0 0
> 11 3 4 0 1 0

 > dfrm$sel <- ave(dfrm$result, dfrm$group, FUN=function(x) x[1]==0 &x[2]==0 & sum(x[3:length(x)]==1)==1)
 > dfrm$sel
  [1] 0 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0
 > dfrm

    group subject result v4 v5 sel

1      1       1      0  1  0   0
2      1       2      1  0  0   0
3      1       3      0  0  0   0
4      1       4      1  0  0   0
5      2       1      0  1  1   0
6      2       2      0  0  1   0
7      2       3      0  1  1   0
8      3       1      0  1  0   1
9      3       2      0  0  1   1
10     3       3      1  0  0   1
11     3       4      0  1  0   1
12     4       1      1  0  0   0
13     4       2      1  1  0   0
14     4       3      0  0  1   0
15     4       4      0  0  0   0
16     4       5      1  0  1   0

Using `subset` should be trivial from this point.

-- 

David Winsemius, MD
West Hartford, CT

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