MATLAB: How to find X unique combinations (order doesn’t matter) of X numbers within an array of X numbers.

jackniferandomsampleresample

The question is in the title.

Thanks!

Best Answer

You might just miss the feature of NCHOOSEK that can accept the vector array as input

>> X=rand(1,5)
X =
    0.3566    0.3205    0.8137    0.1779    0.9431
>> nchoosek(X,3)
ans =
    0.3566    0.3205    0.8137
    0.3566    0.3205    0.1779
    0.3566    0.3205    0.9431
    0.3566    0.8137    0.1779
    0.3566    0.8137    0.9431
    0.3566    0.1779    0.9431
    0.3205    0.8137    0.1779
    0.3205    0.8137    0.9431
    0.3205    0.1779    0.9431
    0.8137    0.1779    0.9431

Related Solutions

MATLAB: Generate large nchoosek in batches

No. Nchoosek is not written in any way to allow you to choose only some reduced subset. In fact, the set of 200 bit binary numbers has a HUGE number of subsets with 5 bits set. I debated showing you how to write such a code, but then you would immediately want to compute combinations of 6 or 7 or 50 of the elements from that set in batches, and you would very quickly overwhelm even a batched version.

The set of combinations that you want to generate gets HUGE, and does so very quickly.

I'll relent just a tiny bit though. The set that you want to generate is simple enough to compute.

Consider if bit 1 is set. Then you need to generate all sets of 199 bits, with exactly 4 of them chosen. You already know how to do this. If bit 1is not set, then you need to generate all possible subsets of 5 bits, choosing from 199 bits. So you can do the whole thing recursively, until the sets become small enough to generate.

MATLAB: Assign column vector to a matrix row

Yes, it is legal. From the documentation on SUBSASGN:

" For multidimensional arrays, a(I,J,K,...) = b assigns b to the specified elements of a. b must be length(I)-by-length(J)-by-length(K)-... or be shiftable to that size by adding or removing singleton dimensions. "

Here's another example where the mis-shaped right hand side of the assignment isn't even a vector,

    >> mat=zeros(4); a=rand(1,1,2,3);
    >> mat(1:2,1:3)=a
    mat =
        0.1779    0.8754    0.5206         0
        0.5702    0.1890    0.4129         0
             0         0         0         0
             0         0         0         0

Best Answer

Related Solutions

MATLAB: Generate large nchoosek in batches

MATLAB: Assign column vector to a matrix row

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