[R] Help wit matrices

[(Ted Harding)]

On 10-Aug-07 18:05:50, Lanre Okusanya wrote:
> Hello all,
> 
> I am working with a 1000x1000 matrix, and I would like to return a
> 1000x1000 matrix that tells me which value in the matrix is greater
> than a theshold value (1 or 0 indicator).
> i have tried
>   mat2<-as.matrix(as.numeric(mat1>0.25))
> but that returns a 1:100000 matrix.
> I have also tried for loops, but they are grossly inefficient.
> 
> THanks for all your help in advance.
> 
> Lanre

Simple-minded, but:

> S<-matrix(rnorm(25),nrow=5)
> S
           [,1]        [,2]       [,3]       [,4]       [,5]
[1,] -0.9283624 -0.44418487  1.1174555  1.9040999 -0.4675796
[2,]  0.2658770 -0.28492642 -1.2271013 -0.5713291  1.8036235
[3,]  0.7010885 -0.42972262  0.7576021  0.3407972 -1.0628487
[4,] -0.2003087  0.87006841  0.6233792 -0.9974902 -0.9104270
[5,]  0.2729014  0.09781886 -1.0004486  1.5987385 -0.4747125
> T<-0*S
> T[S>0.25] <- 1+0*S[S>0.25]
> T
     [,1] [,2] [,3] [,4] [,5]
[1,]    0    0    1    1    0
[2,]    1    0    0    0    1
[3,]    1    0    1    1    0
[4,]    0    1    1    0    0
[5,]    1    0    0    1    0

Does this work OK for your big matrix?

HTH
Ted.

--------------------------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 10-Aug-07                                       Time: 19:50:37
------------------------------ XFMail ------------------------------