# [R] Vectorizing a "for" loop

Petr Pikal petr.pikal at precheza.cz
Thu Aug 3 16:24:30 CEST 2006

```Hi

outer(rows, columns, function(x,y) abs(x-y))
shall do it.

HTH
Petr

On 3 Aug 2006 at 10:10, Daniel Gerlanc wrote:

Date sent:      	Thu, 3 Aug 2006 10:10:46 -0400
From:           	"Daniel Gerlanc" <dgerlanc at gmail.com>
To:             	r-help at stat.math.ethz.ch
Subject:        	[R] Vectorizing a "for" loop
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> Hello all,
>
> Consider the following problem:
>
> There are two vectors:
>
> rows <- c(1, 2, 3, 4, 5)
> columns <- c(10, 11, 12, 13, 14)
>
> I want to create a matrix with dimensions length(rows) x
> length(columns):
>
> res <- matrix(nrow = length(rows), ncol = length(columns))
>
> If "i" and "j" are the row and column indexes respectively, the values
> of the cells are abs(rows[i] - columns[j]).  The resultant matrix
> follows:
>
>      [,1] [,2] [,3] [,4] [,5]
> [1,]    9   10   11   12   13
> [2,]    8    9    10   11   12
> [3,]    7    8      9   10   11
> [4,]    6    7      8     9   10
> [5,]    5    6      7     8    9
>
> This matrix may be generated by using a simple "for" loop:
>
> for(i in 1:length(rows)){
>   for(j in 1:length(columns)){
>     res[i,j] <- abs(rows[i] - columns[j])
>   }
> }
>
> Is there a quicker, vector-based approach for doing this or a function
> included in the recommended packages that does this?
>
> Thanks!
>
> -- Dan Gerlanc
> Williams College
>
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