Hi all

Maybe it is somewhere in the documentations but I havent been able to find it. Is there a simple way to access/assigning to substructure similar to the expression

Code: Select all

b = bit-array in whatever convenient structure;
a[b] = something;


Similar to matlabs

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b = (a == 0);
a(b) =something;

Thanks,

Leon

further digging into the forum, it seems that there is not simple way to perform the action above.

Just for reference, IT++ seems to provide something along this line and it is also a template matrix library.

http://itpp.sourceforge.net/current/users_guide.html

Seems like what you're after is select().

http://eigen.tuxfamily.org/dox/classEig ... 24a4884807

search this forum for usage examples.

bjacob wrote:Seems like what you're after is select().

http://eigen.tuxfamily.org/dox/classEig ... 24a4884807

search this forum for usage examples.

Your answer has always been very helpful. Thank you very much for your time.
Select() does some of what I need but I ultimately wants to have the reference to the SUB-matrix based on the bool vec. This might be difficult in c++ because the size of the resulting matrix is only known at run-time and the pattern of boolean vector is not determined at compile-time.


Something like

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>> a  = rand(3)
a =
    0.9049    0.1111    0.5949
    0.9797    0.2581    0.2622
    0.4389    0.4087    0.6028
>> b = rand(1,3)>0.5
b =
     1     0     0
>> a(b,:)
ans =
    0.9049    0.1111    0.5949 //which is a submatrix reference to a



Sorry, you have to construct that by hand with a for loop. The good news is that this isn't going to be slower than anything we could do within Eigen (e.g. this is not vectorizable anyway).

bjacob wrote:Sorry, you have to construct that by hand with a for loop. The good news is that this isn't going to be slower than anything we could do within Eigen (e.g. this is not vectorizable anyway).

Fair enough. Thanks!