# [R] indexing a vector

Erin Hodgess hodgess at uhddx01.dt.uh.edu
Tue May 8 05:30:56 CEST 2001

```Hi Jeff!

Try this:

which(mymatrix == 4, arr.ind=TRUE)

Hope this help!
Sincerely,
Erin M. Hodgess, Ph.D.
Associate Professor
Department of Computer and Mathematical Sciences
University of Houston - Downtown
One Main Street
Houston, TX 77002
e-mail: hodgess at uhddx01.dt.uh.edu

Subject: Re: [R] indexing a vector
charset="iso-8859-1"
> > Dear R-List,
> >
> > How can one look up the row/column number for a given value in a matrix
or
> > data.frame?  For example in a matrix that contains only unique values
for
> > in [,1] how can I find value x in [,1] and report its row number?
> >
>
> match(x,matrix[,1])
>
> -thomas

As a follow up to this question,  what's the easiest way to
find the column and row indicies for a specified value in a matrix,
when you don't know which column it's in (as assumed above)?

So if   mymatrix <- matrix(c(3, 2, 4, 1), nrow = 2),  what's the easiet
way
to see that the value 4 is in position (1, 2) ?

Thanks much,

Jeff Miller

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```