Re: matrix manipulation question

[David L Lorenz <lorenz@usgs.gov>]

Felipe,
  Use apply instead of a for loop.
 Here's an example of a function that should work. Note that apply
returns a matrix that would need to be transposed.

apply(matrix(c(
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,1,2,3,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,
4,5,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
2,3,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
1,2,3,4,5,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,1,2,3,4,5,0,0,0,0,0,0),
ncol=17, byrow=T), 1, 
FUN = function(x) {
        one
<- match(1, x, nomatch=0)
        return(c(rep(1,one),
rep(0,length(x)-one)))
})

Dave

Jordão, Felipe <Felipe.Jordao@moodys.com> Sent by: s-news-owner@lists.biostat.wustl.edu 07/20/2005 10:16 AM

To:        <s-news@lists.biostat.wustl.edu>         cc:                 Subject:        [S] matrix manipulation question

Hi all,

I have a matrix with some numbers (0:5). The number sequence usually begins
with 1, but if starts in column 1 it can begin with another number. Once
started it will go sequentially with no 0s in the middle, then go back
to 0s. I want to do the following for each row:

1. If the sum of the row is zero, leave it as all 0s (i.e. it's blank to
begin with, then leave it blank)
2. If the sum of the row is not zero, continue and do the following
3. Fill it with 1s until I hit the first "1", fill it with zeroes
thereafter

Here is an example:

Start Matrix
00000000000000000
00001230000000000
00000000100000000
45000000000000000
23400000000000000
12345000000000000
00000012345000000
...

End Matrix
00000000000000000
11111000000000000
11111111100000000
00000000000000000
00000000000000000
10000000000000000
11111110000000000
...

It is a large enough matrix that I get a memory error if I use for loops
(about 30x10000). I also need to keep the ordering of the rows, so if I
start doing things like breaking it up in chunks it has to be put back
properly.

I appreciate any suggestions.

thanks in advance,
Felipe




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