R help - May 2001 - indexing a vector

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?

TIA,

David

S. David White
sdavidwhite at bigfoot.com
Columbus, Ohio

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On Mon, 7 May 2001, David White wrote:
>
> 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

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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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