[R] Help on efficiency/vectorization
Gerrit Eichner
Gerrit.Eichner at math.uni-giessen.de
Thu Aug 27 08:32:56 CEST 2009
Hi, Steven,
try
lapply( x, function( v) rownames(x)[ v == 1])
or
lapply( x, function( v, rn) rn[ v == 1], rn = rownames( x)))
which is faster.
Regards -- Gerrit
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AOR Dr. Gerrit Eichner Mathematical Institute, Room 305 E
gerrit.eichner at math.uni-giessen.de Justus-Liebig-University Giessen
Tel: +49-(0)641-99-32104 Arndtstr. 2, 35392 Giessen, Germany
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On Thu, 27 Aug 2009, Steven Kang 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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