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matrix manipulation question

To: <s-news@lists.biostat.wustl.edu>
Subject: matrix manipulation question
From: Jordão, Felipe <Felipe.Jordao@moodys.com>
Date: Wed, 20 Jul 2005 11:16:07 -0400
Thread-index: AcWNPfPmUM8NVGfXTceXkNhYoRr/kg==
Thread-topic: 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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