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Re: Fast matrices comparison

  • To: mathgroup at smc.vnet.net
  • Subject: [mg115913] Re: Fast matrices comparison
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Tue, 25 Jan 2011 06:31:02 -0500 (EST)


On 25 Jan 2011, at 10:19, JJ wrote:

> Hi MathGroup
>
> I have to compare two big matrices (in the SparseArray form), say m1 and m2.
> I need that the elements of m1 will be replaced by 0 if they are less or
> equal to
> the corresponding elements of m2.
>
> For example, if m1={{8,7},{3,9}} and m2={{2,3},{4,5}},
> I would like to have m1={{8,7},{0,9}} because m1[[2,1]]<m2[[2,1]].
>
> I can do it easily with two nested for loops but I think it is not an
> efficient way to do it.
> I was wondering if somebody knows how to do it using a fast conditional
> replacement rule and/or pure functions.
>
> Thank you.
>
>
I think the following ought to be quite fast but I have not tried comparing it to any alternatives:

m1*(UnitStep[m1 - m2])

Andrzej Kozlowski


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