low speed of 'ismember' function
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hi. in my code there is a for loop like the following:
for i=1:n
N=find(~ismember(Vector1,Vector2))
do something...
end
This loop is repeated several thousand times. 'ismember' function is very slow. So that most of the runtime for 'ismember' function lost. Is there any alternative to this?
回答（3 个）
Johan Löfberg
2014-8-29
0 个投票
If data is sorted, using ismembc could be a quick fix.
2 个评论
Ehsan
2014-8-29
Johan Löfberg
2014-8-29
Then I would scratch ismember and do sort+ismembc (ismember contains a lot of overhead. look into it and you will see that it basically does sort+ismembc once all data is checked etc)
David Sanchez
2014-8-29
Depending on your data, you might try to code your own function avoiding some conditions and calls to sub-functions within the ismember function.
You can take a look at ismember code with:
type ismember
and try to make it easier.
3 个评论
Ehsan
2014-8-29
José-Luis
2014-8-29
The way you use ismember() seems to be inefficient. You are going to be processing similar things over and over. You could instead loop through the variable of interest, do an exhaustive search, save that somewhere and then %do something based on those results.
Ehsan
2014-8-29
Titus Edelhofer
2014-8-29
Hi,
does "Vector1" and "Vector2" changes in every iteration? Often you see something like
for i=1:n
v = ismember(x(i), y);
% do something
end
which can be changed to
vAll = ismember(x, y);
for i=1:n
% now do something with vAll(i)
end
Titus
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