[R] Matrix manipulation - dropping rows based on a query

Uwe Ligges
Tue, 22 Jul 2003 19:40:52 -0000

James MacDonald wrote:
> tst <- apply(my.mat, 2, mean) < 1

... and
  rowMeans(my.mat) < 1
will be faster, but perhaps not working for the requested "more
complicated query".

Uwe Ligges

> my.mat[,tst]
>
> Will return only columns with mean < 1
>
> Jim
>
>
>
> James W. MacDonald
> Affymetrix and cDNA Microarray Core
> University of Michigan Cancer Center
> 1500 E. Medical Center Drive
> 7410 CCGC
> Ann Arbor MI 48109
> 734-647-5623
>
>
>>>><monkeychump at hushmail.com> 07/22/03 01:53PM
>>>
>
>
> I have a matrix with some very funky data. I want to drop the columns
> with a mean > 1 (for instance).
> #Example:
> my.mat <- matrix(rnorm(100, 0, 3), nrow = 10)
>
> #I know I can get the row means:
> apply(my.mat,1, mean)
>
> I think I need to get a vector that has those rows > 1
>
> my.mat[-rows>1,]
>
> The actual querry is much more complicated but this gives an
> approximation.
>
> Thanks.
>