CODEWITHSUNDEEP
r
Jens Henrik
Jens Henrik

Reputation: 99

get values from factor using matrix

I want to extract some values from a factor, but instead of having one index string i have a data.matrix containing multiple columns, all containing indexes.

I have:

f<-factor(c('a','b','c','a'))
d<-data.matrix(data.frame(t=c(1,3,2),u=c(2,3,4)))
> f[d]
[1] a c b b c a

But instead of having all return values in one vector, I would like to maintain the data.matrix structure like this:

[,1][,2]
a   b
c   c
b   a

How is this possible i en elegant way?

Upvotes: 2

Views: 117

Answers (1)

A5C1D2H2I1M1N2O1R2T1
A5C1D2H2I1M1N2O1R2T1

Reputation: 193517

I'm not sure of the definition of elegant, but you are essentially looking for dim().

You can do this in a cryptic way with dim<-(), like this:

`dim<-`(f[d], dim(d))
##      [,1] [,2]
## [1,] a    b   
## [2,] c    c   
## [3,] b    a   
## Levels: a b c

Less cryptic would be the following (though note the slight difference in the result).

matrix(f[d], ncol = ncol(d))
##      [,1] [,2]
## [1,] "a"  "b" 
## [2,] "c"  "c" 
## [3,] "b"  "a"

If you're after a data.frame, then try:

as.data.frame.matrix(`dim<-`(f[d], dim(d)))
##   V1 V2
## 1  a  b
## 2  c  c
## 3  b  a

Or data.frame(matrix(f[d], ncol = ncol(d))).

Upvotes: 4

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