Message-ID: <Pine.LNX.4.64.0612101955090.3078@tajo.ucsd.edu>
Date: 2006-12-11T04:00:57Z
From: Charles C. Berry
Subject: sample "n" random positions from a matrix
In-Reply-To: <687436.75963.qm@web56612.mail.re3.yahoo.com>
On Sun, 10 Dec 2006, Milton Cezar Ribeiro wrote:
> Hi there,
>
> I have a binary matrix (dim 100x100) filled with values 0 and 1. I need
> select a record "n" positions of that matrix when values are 1. How can
> I do that?
>
Is this what you want?
> mat.100 <- diag(100) # just for instance
> n <- 7 # supposing you want 7
> which( mat.100==1, arr.ind=T )[ sample( 100, n ), ]
row col
[1,] 99 99
[2,] 93 93
[3,] 36 36
[4,] 74 74
[5,] 11 11
[6,] 3 3
[7,] 21 21
>
[...]
Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu UC San Diego
http://biostat.ucsd.edu/~cberry/ La Jolla, San Diego 92093-0717