[R] corresponding replicated el of one matrix in another matrix or vector

[Uwe Ligges]

On 23.07.2014 21:16, carol white wrote:
> Hi,
> I have a matrix of unique elements (strings) like v1 and a vector which contains replicated values of the 2nd column of the first matrix.
>
> v1 = cbind(c("1","2","3"),c("a","b","c"))
>
> v2 = c(rep("a",5), rep("c",10), rep("b",3))
>
> How can I add a column to v2 that contains the values of the first column of the first matrix v1 where the 2nd column of v1 matches the values of v2? Do I need to grep by looping over the nrow of v1 which is very time consuming or is there a better solution?
>
> the results should be the same as
>
>
> v3=rbind( c(rep("a",5), rep("c",10), rep("b",3)), c(rep("1",5), rep("3",10), rep("2",3)))


I'd try

t(merge(data.frame(V2=v2), as.data.frame(v1)))


Best,
Uwe Ligges


> ---------------------------------------------------------------
> v1
>       [,1] [,2] [,3]
> [1,] "1"  "2"  "3"
> [2,] "a"  "b"  "c"
>> v2
>   [1] "a" "a" "a" "a" "a" "c" "c" "c" "c" "c" "c" "c" "c" "c" "c" "b" "b" "b"
>> v3
>       [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14]
> [1,] "a"  "a"  "a"  "a"  "a"  "c"  "c"  "c"  "c"  "c"   "c"   "c"   "c"   "c"
> [2,] "1"  "1"  "1"  "1"  "1"  "3"  "3"  "3"  "3"  "3"   "3"   "3"   "3"   "3"
>       [,15] [,16] [,17] [,18]
> [1,] "c"   "b"   "b"   "b"
> [2,] "3"   "2"   "2"   "2"
> 	[[alternative HTML version deleted]]
>
>
>
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