Can I speed up an ismember operation?
3 vues (au cours des 30 derniers jours)
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I have a list of 100 random numbers 1-10:
numpoints = 100;
gridnum = 10;
grid_ind = randi(gridnum,[numpoints 1]); % 100 points in 10 random cells
and each of the 10 possible values has a corresponding list (of random length) of values, which are indexes to grid_ind:
for i=1:gridnum
neighbgrids{i} = randi(numpoints,[randi(5) 1]);
end
So far, so good. Now, I need to find the indexes for all elements in grid_ind which have the same values as in each cell list in neighbgrids. So I use:
for i=1:numpoints
neighblist{i} = find(ismember(grid_ind,neighbgrids{grid_ind(i)}));
end
But this turns out to be very slow. Is there a faster way to do this part?
5 commentaires
Réponse acceptée
Matt J
le 1 Fév 2015
Modifié(e) : Matt J
le 1 Fév 2015
This should speed things up.
for i=1:gridnum
neighblist{i} = find(ismember(grid_ind,neighbgrids{i}));
end
neighblist=neighblist(grid_ind);
I see a 10x speed-up over your originally posted example.
2 commentaires
Matt J
le 1 Fév 2015
It seems inefficient to be using find(). The output of ismember is enough to index into grid_inds and then you could maintain neighblist as a matrix instead of a cell, which is more efficient:
neighblist=zeros(gridnum,numpoints);
for i=1:gridnum
neighblist(i,:) = ismember(grid_ind,neighbgrids{i});
end
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