# Re: [R] matching matrix columns to a vector

From: David Winsemius <dwinsemius_at_comcast.net>
Date: Mon, 24 Nov 2008 12:47:52 -0500

Since negative values could balance positives, you might need to use: which(colSums(abs(t-v)) == 0)

``` > t=matrix(1:12,3,4)
> v=c(1,2,3)
> which(colSums(t-v) == 0)
```

 1
> t

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

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

> t[1,2] <- -5
> which(colSums(t-v) == 0)
 1 2

> which(colSums(abs(t-v)) == 0)
 1

--
David Winsemius
Heritage Labs

On Nov 24, 2008, at 11:59 AM, <Jagat.K.Sheth_at_wellsfargo.com> <Jagat.K.Sheth_at_wellsfargo.com  > wrote:

> How about which(colSums(t-v) == 0) ?
>
> -----Original Message-----
> From: r-help-bounces_at_r-project.org [mailto:r-help-bounces_at_r-project.org
> ]
> On Behalf Of Salas, Andria Kay
> Sent: Monday, November 24, 2008 10:04 AM
> To: r-help_at_r-project.org
> Subject: [R] matching matrix columns to a vector
>
> 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
> 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)
>  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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