# [R] Excluding rows from a matrix

ben@zoo.ufl.edu ben at zoo.ufl.edu
Mon Aug 21 18:52:05 CEST 2000

```On Mon, 21 Aug 2000, [iso-8859-1] José Ernesto Jardim wrote:

> Hi
>
> I have a matrix (4 x 950) and I want to remove 3 rows, where the values
> from the first column are 713, 714 and 715. I can select the rows, one
> by one, with
>
> mat[mat\$first==713,]
> mat[mat\$first==714,]
> ...
>
> but I'm unable to (i) select the 3 rows at once, (ii) select the matrix
> excluding those rows.
>

The hard way (if you had non-contiguous rows): using "|" (logical or)

mat[mat\$first==713 | mat\$first==714 | mat\$first==715,]

OR

mat[mat\$first>=713 & mat\$first<=715,]

If you were going to do a lot of this you could define a "between"
function

between <- function(x,lower,upper) {
x>=lower & x<= upper
}

mat[between(mat\$first,713,715),]

To get all the other rows use ! (not), for example

mat[!between(mat\$first,713,715),]

see the "Logical Operators" page in the R documentation.

Ben Bolker

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```