[R] matching matrix columns to a vector
David Winsemius
dwinsemius at comcast.net
Mon Nov 24 19:02:02 CET 2008
Consider:
> apply(t,2,function(x)identical(x,v))
[1] TRUE FALSE FALSE FALSE
> apply(t,2,function(x)identical(x,v))+0
[1] 1 0 0 0
and if you wanted to get the position you could use which:
> which(apply(t,2,function(x)identical(x,v)))
[1] 1
> t[,4] <- v
> which(apply(t,2,function(x)identical(x,v)))
[1] 1 4
--
David Winsemius
On Nov 24, 2008, at 11:03 AM, Salas, Andria Kay wrote:
> I need help with (hopefully) just one more thing. I have been
> fussing with this for quite some time and have decided just to give
> up and ask! I want to match a column in a matrix to a vector. I
> found a "which" command that I thought would be helpful as it does
> the following:
>
>> g=c(1,5,3,2,7)
>> which(g==5)
> [1] 2
>
> As the above gave which placement in the g vector corresponded to 5
> (the second place), I need this command to give me which column in a
> matrix matches to a vector.
>
> This is just a toy example of what I am trying to do:
>> t=matrix(1:12,3,4)
>> v=c(1,2,3)
>> which(t[,j]==v)
>
> This does not work, and with my "real" matrices and vectors, I was
> getting outputs that did not make sense. These examples are more to
> give an idea of what I am aiming to accomplish.
>
> Thank you for all the help!!
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