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MathGroup Archive 2007

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Re: Logical comparisons of items in a two lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg75480] Re: [mg75446] Logical comparisons of items in a two lists
  • From: Carl Woll <carlw at wolfram.com>
  • Date: Wed, 2 May 2007 03:54:57 -0400 (EDT)
  • References: <200705010722.DAA07278@smc.vnet.net>

actuary at mchsi.com wrote:

>Hello:
>
>I have two lists of real numbers, a & b.  I want two compare
>individual items in one list to the corresponding items in the other
>list.  For example Is a[[1]] > b[[1]]. At the end of the comparisons,
>I want to count the "Trues".  I know how to do this use a "Table"
>statement and a "Count" statement.  Is there a quicker, more efficient
>way of counting the number of "Trues".
>
>Thanks
>
>Larry
>
>  
>
I would do this using UnitStep. Here is some test data:

d1=Table[Random[],{10^6}];
d2=Table[Random[],{10^6}];

Here is the UnitStep approach:

Total[UnitStep[d1-d2]]//Timing
{0.203 Second,500735}

Here is an approach similar to using Table and Count:

Count[Thread[d1>d2],True]//Timing
{3.172 Second,500735}

Carl Woll
Wolfram Research


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