Selecting elements of logically pruned vector (concatenating indices)

Ced
2015 1 12
2 个回答
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更新时间：2015 1 12
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Hi
Given a vector b and a logical vector v_log, is there a straightforward way to extract particular indices of the partial vector b(v_log) without saving it?
In code:
b = randn(20,1); % a vector
v_log = (randn(20,1)>0); % logical vector to select parts of b
ind = [ 2 ; 3 ]; % the elements I'm interested in
c = b(v_log)(ind); % This does not work, but is there a way to do this?
Thanks!

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 采纳的回答

Kelly Kearney
Kelly Kearney 2015-1-12

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I think you'd need to save the indices.
idx = find(v_log);
c = b(idx(ind));
Depending on the size/sparsity of v_log, you may be able to save some time and storage space by only saving the necessary number of indices:
idx = find(vlog, max(ind), 'first');
c = b(idx(ind));

更多回答（1 个）

Ced
Ced 2015-1-12
编辑：Ced 2015-1-12

0 个投票

@Star Strider: Sure thing, thanks. Just for clarity: b is an arbitrary vector. v_log is a logical vector, hence b(v_log) returns a part of b. My question was how to extract certain elements with indices ind of that partial vector b(v_log) without having to save them.
@Kelly Kearney: Thanks, I'll accept that answer and give that a try. The size of v_log in my case is pretty (very) large and is computed in an iterative loop, which is why I was hoping to do this without saving.

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