MATLAB: Can I speed up an ismember operation

ismemberMATLAB

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?

Best Answer

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.
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