From: Marc Schwartz <marc_schwartz_at_comcast.net>

Date: Mon, 24 Nov 2008 12:04:29 -0600

> [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:
*

*>
*

> 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!!
*

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 25 Nov 2008 - 04:48:41 GMT

Date: Mon, 24 Nov 2008 12:04:29 -0600

on 11/24/2008 10:03 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

>> 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

Presuming that you are comparing integers or characters:

mat <- matrix(1:12, 3, 4)

Vec <- 1:3

*> mat
*

[,1] [,2] [,3] [,4]

[1,] 1 4 7 10 [2,] 2 5 8 11 [3,] 3 6 9 12

*> Vec
*

[1] 1 2 3

> which(apply(mat, 2, identical, Vec))

[1] 1

Another possible option:

> which(apply(mat, 2, function(x) all(x == Vec)))

[1] 1

See ?apply, ?identical and ?all

Note that a variation on this would be required for floating point numbers using all.equal().

You might also want to add error checking to be sure that:

length(Vec) == nrow(mat)

lest you risk re-cycling of values.

**HTH,
**
Marc Schwartz

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 25 Nov 2008 - 04:48:41 GMT

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