# [R] Help on efficiency/vectorization

jim holtman jholtman at gmail.com
Thu Aug 27 14:03:34 CEST 2009

```try this:

> 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  0  1  0  0  1  0  0  0   1
b  1  0  0  0  1  1  1  1  0   0
c  0  1  0  1  0  0  0  0  1   0
d  0  1  0  0  0  1  0  0  1   1
e  0  0  1  1  0  1  1  0  1   1
> lapply(names(x), function(z) rownames(x)[x[[z]] == 1])
[[1]]
[1] "b"

[[2]]
[1] "c" "d"

[[3]]
[1] "a" "e"

[[4]]
[1] "c" "e"

[[5]]
[1] "b"

[[6]]
[1] "a" "b" "d" "e"

[[7]]
[1] "b" "e"

[[8]]
[1] "b"

[[9]]
[1] "c" "d" "e"

[[10]]
[1] "a" "d" "e"

>

On Thu, Aug 27, 2009 at 2:13 AM, Steven Kang<stochastickang at 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]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> and provide commented, minimal, self-contained, reproducible code.
>

--
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

```