Try this also:

lapply(apply(x == 1, 2, which), names)

On Thu, Aug 27, 2009 at 3:13 AM, Steven Kang <stochastickang@gmail.com>wrote:

> Dear R users,
>
> I am trying to extract the rownames of a data set for which each columns
> meet a certain criteria. (condition - elements of each column to be equal
> 1)
>
> I have the correct result, however I am seeking for more efficient (desire
> vectorization) way in implementing such problem as it can get quite messy
> if
> there are hundreds of columns.
>
> Arbitrary data set and codes are shown below for your reference:
>
> x <- as.data.frame(matrix(round(runif(50),0),nrow=5))
>
> rownames(x) <- letters[1:dim(x)[1]]
>
> > x
>  V1 V2 V3 V4 V5 V6 V7 V8 V9 V10
> a  0  1   1    1   0   0    0   0   1    0
> b  1  1   1    1   0   1    0   0   1    1
> c  0  1   1    0   0   0    0   0   0    1
> d  1  0   0    1   1   1    1   1   0    0
> e  1  0   0    0   0   1    1   0   1    0
>
> V1.ind <- rownames(x)[x[,"V1"]==1]
> V2.ind <- rownames(x)[x[,"V2"]==1]
> V3.ind <- rownames(x)[x[,"V3"]==1]
> V4.ind <- rownames(x)[x[,"V4"]==1]
> :
> :
> V10.ind <- rownames(x)[x[,"V10"]==1]
>
> > V1.ind
> [1] "b" "d" "e"
> > V2.ind
> [1] "a" "b" "c"
> > V3.ind
> [1] "a" "b" "c"
> :
> :
> > V10.ind
> [1] "b" "c"
>
>
>
> Your expertise in resolving this issue would be highly appreciated.
>
>
> Steve
>
>        [[alternative HTML version deleted]]
>
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> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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