在Matlab中的列表中选择一个随机非零元素的索引

Question

Is there any ready command to get the intended output from the input?

Input

>>> a=[1 0 3 0 5 6 7 8 0 10 0 0]; selectNonZero(a)

Intended output

1 or 3 or 5 or 6 or 7 or 8 or 10

Trials

>> b=a(a~=0); pi=randi([1, length(b)]); b(pi)    % The original index of b(pi)?

>> fix=[0 1 2 2 2 2 2]; pi+fix(pi)               % Fix changed index, cum command?

Answer 1

You can do it this way. It's similar to your approach, but using find to know the indices of nonzero values.

jj = find(a~=0); % indices of nonzero values of a
ind = jj(randi(length(jj))); % randomly pick one of those indices
val = a(ind); % corresponding value of a

The results you want are sel (selected value) and ind (its index within a ).

Answer 2

A variant of Luis' answer is to use the built-in nnz function:

idx = find(a);
rand_idx = idx(randi(nnz(a)));

If you have the Statistics Toolbox installed, you can reduce this into a one-liner using randsample :

rand_idx = randsample(find(a), 1);

Note: if you want to choose a random value (and not its index), replace find(a) with nonzeros(a) (this is a shorter alternative to generating a random index and then doing a(rand_idx) ).