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Re: Table of tables

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113292] Re: Table of tables
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Fri, 22 Oct 2010 01:36:23 -0400 (EDT)

On Oct 21, 2010, at 7:01 AM, Luiz Melo wrote:

>
> Thanks Sebastian and Valeri for the help.
>
> I'm actually looking for a function that operates only on the third row of each
> column-matrix terms(which happen to be complex in the example I gave), but
> leaves the other terms intact. Consider a different example:
>
> Let
> t == {{{-1, -1, -2}, {-1, -1, -3}}, {{-1, -1, -4}, {-1, -1, -5}}};
>
> how can I get
>
> {{{-1, -1, 2}, {-1, -1, 3}}, {{-1, -1, 4}, {-1, -1, 5}}};
>
> that is, in this case, I need a function that takes the Abs[] of the 3rd row of
> each sub-matrix and leaves the other terms intact.

MapAt[Abs, t,
 Flatten[Table[{i, j, 3}, {i, First[Dimensions[t]]}, {j, Dimensions[t][[2]]}],
   1]]

More generally

mapAtColumn[t_,column_,f_]:==Module[{d},MapAt[f,t,Flatten[Table[Append[Table[d[i],{i,ArrayDepth[t]-1}],column],Evaluate[Sequence@@Table[{d[i], Dimensions[t][[i]]},{i,ArrayDepth[t]-1}]]],ArrayDepth[t-2]]]]

will map f onto the last position column of a multidimensional array t.  This can be further generalized to map onto a single value of a particular dimension and all other dimensional values.

Regards,
	Ssezi

>> Hi Luiz!
>>
>> Luiz Melo wrote:
>>> Given
>>>
>>> t == {{{-1, -1, -2+2I}, {-1, -1, 3-I}}, {{-1, -1, 4+I}, {-1, -1, -5-5I}}};
>>>
>>> how can I extract the imaginary part of the complex elements to obtain
>>>
>>> {{{-1, -1, 2}, {-1, -1, -1}}, {{-1, -1, 1}, {-1, -1, -5}}};
>>
>> What about:
>>
>> Function[{e}, If[Im[e] ==== 0, e, Im[e]], Listable][t]
>>
>> There seems to be no ComplexQ therefore I test with "Im[e] ==== 0" if it
>> is not a complex number.
>>
>> Cheers,
>>
>> Sebastian
>>
>
>
> --
>
>


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