Using find with a vector without having to use a for loop
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I have code which does
for t = 1: length(vector2)
idx(t) = find(vector <=vector2(t), 1, 'last');
end
Can I call find.m without using a for loop (or bsxfun.m) and if so how?
Or should I just use histc?
[~,idx]=histc(vector2, vector);
5 个评论
the cyclist
2013-3-14
Why do you prefer not to use bsxfun? It seems well suited to the task.
Matlab2010
2013-3-14
Friedrich
2013-3-14
That is not true! BSXFUN is highly parallized under the hood. Fastest function you can get.
Jan
2013-3-14
BSXFUN is not a slower version of a loop. I think ARRAYFUN could earn this description, especially when used with anonymous functions.
Matlab2010
2013-3-28
采纳的回答
Hi,
use bsxfun and make sure one vector is a row vector and the other a column vector (a would be vector and b would be vector2)
a = [1 2 3 4 5 6]
b = [ 1 5 8 3 -10 2]
idx = bsxfun(@le,a',b)
Now you need to get a bit tricky I guess:
tmp = idx*(10.^[1:numel(b)]')
floor(log10(tmp))
Not sure if maybe log2 would be faster, you would need to try it:
tmp = idx*(2.^[1:numel(b)]')
floor(log2(tmp))
2 个评论
Jan
2013-3-14
POWER and LOG10 are expensive functions. There must be a solution based on the integer indices also.
Jan
2013-3-14
Yes! When the input vector2 (as in the original question) is sorted (and find(., 1, 'last') implies that it is), the logical matrix created by bsxfun contains zeros on the left and ones on the right (or top and bottom?). Then this matrix can be reshaped to a row vector and strfind searchs for [false true]. Finally the resulting indices must be cleaned up using mod() with the number of columns.
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2013-3-14
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