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Re: Simply but handy question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124846] Re: Simply but handy question
  • From: Barrie Stokes <Barrie.Stokes at newcastle.edu.au>
  • Date: Thu, 9 Feb 2012 05:39:03 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201202081029.FAA06451@smc.vnet.net>

Hi Paul

How about:

y = {{a, b}, {0, c}};

ClearAll[ somethingOrZero]  
somethingOrZero[x_] := If[ SameQ[ x, 0 ], 0, 1 ]

Map[ somethingOrZero, y, {2} ].

Check the online Help for what the parameters of Map are, and what SameQ means.

Barrie

>>> On 08/02/2012 at 9:29 pm, in message <201202081029.FAA06451 at smc.vnet.net>,
jediwhelan <jediwhelan at googlemail.com> wrote:
> Dear group members,
> 
> I am new to mathematica (well, I'm not actually but I haven't used it
> in 5 years +).
> 
> Is there an easy way to return a matrix X of 1's and 0's to test
> whether the entries in Y
> are different from zero.
> 
> i.e.,
> 
> if Y = {{a,b},{0,c}}
> 
> Then X would return
> 
> X = {{1,1},{0,1}}
> 
> This would be handy for very large or complicated matrices where one
> would like to know if specific entries are zero?
> 
> Many thanks,
> Paul




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