# [R] Grouping Index of Matrix Based on Certain Condition

Christos Hatzis christos.hatzis at nuverabio.com
Fri Aug 1 05:26:53 CEST 2008

```Try this:

> x <- matrix(runif(20), ncol=2)
> x
[,1]      [,2]
[1,] 0.33119833 0.4797847
[2,] 0.01339784 0.5218626
[3,] 0.78975940 0.8597246
[4,] 0.60849015 0.5217248
[5,] 0.91779777 0.9364047
[6,] 0.88302538 0.3467961
[7,] 0.87565986 0.4029147
[8,] 0.51594479 0.9885018
[9,] 0.87680383 0.7694989
[10,] 0.40761877 0.4661846

> apply(x, 1, function(y) ifelse(diff(y)<0, 1, 2))
[1] 2 2 2 1 2 1 1 2 1 2

-Christos

> -----Original Message-----
> From: r-help-bounces at r-project.org
> [mailto:r-help-bounces at r-project.org] On Behalf Of Gundala Viswanath
> Sent: Thursday, July 31, 2008 11:00 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Grouping Index of Matrix Based on Certain Condition
>
> Hi,
>
> I have the following (M x N) matrix, where M = 10 and N =2
> What I intend to do is to group index of (M) based on this
> condition of "x_mn" , namely
>
> For each M,
> If x_m1 > x_m2, assign index of M to Group1 otherwise assign
> index of M into Group 2
>
>
> > x
>                [,1]       [,2]
>   [1,] 4.482909e-01 0.55170907
>   [2,] 9.479594e-01 0.05204063
>   [3,] 8.923553e-01 0.10764474
>   [4,] 9.295003e-01 0.07049966
>   [5,] 8.880434e-01 0.11195664
>   [6,] 9.197367e-01 0.08026327
>   [7,] 9.431232e-01 0.05687676
>   [8,] 9.460356e-01 0.05396442
>   [9,] 6.053829e-01 0.39461708
>  [10,] 9.515173e-01 0.04848268
>
> Is there a simple way to do it in R?
> - Gundala Viswanath
> Jakarta - Indonesia
>
> ______________________________________________
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> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>

```