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MathGroup Archive 2005

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Re: Count using pattern on two different matrices

  • To: mathgroup at smc.vnet.net
  • Subject: [mg57084] Re: [mg57079] Count using pattern on two different matrices
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sun, 15 May 2005 03:03:38 -0400 (EDT)
  • References: <200505140858.EAA09500@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 14 May 2005, at 17:58, Lee Newman wrote:

> I have two matrices with an equal number of rows, but not necessarily
> columns, for example:
>
> L1= {{True,False},{False, True},{False, False}, etc.....} ;
> L2= {{True,False,False},{True, True,True},{False, True,False}, 
> etc.....} ;
>
> I would like to compute a count of the number of rows in which one of
> the columns of L1 meets some criterion, and one of the columns of L2
> meets some criterion, i.e.  If L1[[row,2 ]]==False  and
> L2[[row,3]]==True  then this row contributes 1 to the count.
>
> I suspect that there is an elegant way to do this, perhaps using 
> Count[]
> and MapThread, but I can't figure it out other than resorting to a
> rather clumsy For or Do loop that would check line by line and maintain
> a counter.
>
> Any help would be appreciated,
> Lee
>
>
Here is one way:

l1 = {{True, False}, {False, True}, {False, False}} ;
l2 = {{True, False, False}, {True, True, True}, {False, True, False}} ;



Count[Transpose[{l1, l2}],
   _?(#1[[1,2]] == False && #1[[2,3]] == True & )]

0

Changing the criterion to L1[[row,2 ]]==False and L2[[row,3]]==False


Count[Transpose[{l1, l2}],
   _?(#1[[1,2]] == False && #1[[2,3]] == False & )]

2

Andrzej Kozlowski


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