Say I have a matrix of:
tmp1 = 5;
tmp2 = 5;
tmp3 = RandomChoice[{0, 1, 2, 3, 4, 5}, {tmp1, tmp2}];
MatrixForm[tmp3]
How to do a conditional operation of elements - 1 if non-zero, else do nothing, as in the attached:
. Maybe using Positive?
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asked Nov 13 '12 at 15:09
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You have lots of options. Among them Replace:
Replace[tmp3, x : Except[0] :> x - 1, {2}]
And numerically for the entire matrix:
tmp3 - Unitize[tmp3]
answered Nov 13 '12 at 15:19
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Another possibility is to use Sign[]. To make each positive element of the matrix decrease by one:
tmp3-Sign[tmp3]
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$\begingroup$ You probably want
Abs@Sign@tmp3, which is the same asUnitize. $\endgroup$ – rm -rf♦ Nov 13 '12 at 16:12 -
$\begingroup$ OPs matrix is all positive integers, so it's the same. But it is not clear what the desired behavior would be if you had negative integers: using Sign[ ] they would all head towards zero; using Unitize the negatives would keep decreasing. $\endgroup$ – bill s Nov 13 '12 at 16:24
tmp3 /. (x_ ?Positive -> x - 1)? $\endgroup$ – b.gates.you.know.what Nov 13 '12 at 15:14tmp3 /. x_?Positive :> x - 1ortmp3 - Boole[Positive[tmp3]]then? $\endgroup$ – J. M. will be back soon♦ Nov 13 '12 at 15:17