You could try either of the two examples below. They both assume that min
and max are invariant:
mymat <- matrix (
c (
1 , 1 , 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 2
, 2 , 2 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 2 , 2 , 2 , 0 , 0
, 0 , 0 , 3 , 3 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 4 , 4 , 3 , 3
, 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0
) , nrow = 5
)
## this way gives same random values for
## each integer between 0 and
## max (mymat):
milton <- function ( x , min = 0.4 , max = 0.7 ) {
.rep <- runif ( n = max ( x ) , min = min , max = max )
for ( i in 1:max ( x ) ) {
x[x == i] <- .rep[i]
}
x
}
milton ( x = mymat )
## this way gives different random values
## for each integer between
## 0 and max (mymat):
milton <- function ( x , min = 0.4 , max = 0.7 ) {
for ( i in 1:max ( x ) ) {
x [ x == i ] <- runif (
sum ( x == i )
, min = min
, max = max
)
}
x
}
milton ( x = mymat )
--
David
-----------------------------------------------------
David Huffer, Ph.D. Senior Statistician
CSOSA/Washington, DC david.huf...@csosa.gov
-----------------------------------------------------
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org]
On Behalf Of milton ruser
Sent: Wednesday, August 26, 2009 1:18 PM
To: David Winsemius
Cc: r-help@r-project.org
Subject: Re: [R] changing equal values on matrix by same random number
Hi David,
Thanks for the reply. This is what I need:
mymat[mymat==1] <- runif(1,min=0.4,max=0.7)
mymat
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11]
[1,] 0.4573161 0 0 2 0 0 0 0 0 3 0
[2,] 0.4573161 0 0 2 0 2 0 0 0 0 0
[3,] 0.4573161 0 0 2 0 2 0 0 4 0 0
[4,] 0.0000000 0 0 0 0 2 3 0 4 0 0
[5,] 0.0000000 0 0 0 0 0 3 0 3 0 0
But as my real landscapes have values from 1 to large number (~10,0000),
so I think that if I put this on a for() looping it will be very time
expensive,
and as I have a lot of landscapes, I need to speed up it.
Any suggestion?
bests
milton
On Wed, Aug 26, 2009 at 1:12 PM, David Winsemius <dwinsem...@comcast.net
wrote:
On Aug 26, 2009, at 12:53 PM, milton ruser wrote:
Dear all,
I have about 30,000 matrix (512x512), with values from 1 to N.
Each value on a matrix represent a habitat patch on my
matrix (i.e. my landscape). Non-habitat are stored as ZERO.
No I need to change each 1-to-N values for the same random
number.
Just supose my matrix is:
mymat<-matrix(c(1,1,1,0,0,0,0,0,0,0,0,
0,0,0,0,2,2,2,0,0,0,0,
0,0,0,0,2,2,2,0,0,0,0,
3,3,0,0,0,0,0,0,0,4,4,
3,3,0,0,0,0,0,0,0,0,0), nrow=5)
I would like that all cells with 1 come to be
runif(1,min=0.4, max=0.7), and cells with 2
be replace by another runif(...).
First the wrong way and then the right way:
mymat[mymat==1] <- runif(1,min=0.4,max=0.7)
mymat
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11]
[1,] 0.4573161 0 0 2 0 0 0 0 0 3 0
[2,] 0.4573161 0 0 2 0 2 0 0 0 0 0
[3,] 0.4573161 0 0 2 0 2 0 0 4 0 0
[4,] 0.0000000 0 0 0 0 2 3 0 4 0 0
[5,] 0.0000000 0 0 0 0 0 3 0 3 0 0
All the values are the same, clearly not what was desired.
Put it back to your starting point:
mymat<-matrix(c(1,1,1,0,0,0,0,0,0,0,0,
+ 0,0,0,0,2,2,2,0,0,0,0,
+ 0,0,0,0,2,2,2,0,0,0,0,
+ 3,3,0,0,0,0,0,0,0,4,4,
+ 3,3,0,0,0,0,0,0,0,0,0), nrow=5)
# So supply the proper number of random realizations:
mymat[mymat==1] <- runif(sum(mymat==1),min=0.4,max=0.7)
mymat
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11]
[1,] 0.5745665 0 0 2 0 0 0 0 0 3 0
[2,] 0.6956418 0 0 2 0 2 0 0 0 0 0
[3,] 0.6935466 0 0 2 0 2 0 0 4 0 0
[4,] 0.0000000 0 0 0 0 2 3 0 4 0 0
[5,] 0.0000000 0 0 0 0 0 3 0 3 0 0
If you want to supply a matrix of max and min values for the other
integers
there would probably be an *apply approach that could be used.
I can do it using for(), but it is very time expensive.
Any help are welcome.
cheers
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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