Multi tool use

How to impliment logical indexing faster in matlab? [closed]

I have several matrices that I need to add to one large matrix. The large matrix (300002x50) is split up by .001 seconds and the timing for the other 49 matricies (14250x2) are roughly .02 apart, but not uniformly distributed. I have tried find to index the entries from the smaller matrices into the larger matrix, but it was too slow. I have since tried:

find

for a = 1:length(test)
aaa = abs(AF1(:,1)-test(a,1))<10^-6;
AF1(aaa,index)=test(a,2);
end


Where test is a 14250x2 double (time,data), AF1 is a 300002x50 double matrix and index is which column in AF1 the data will be added to. It was a bit faster, but it still takes up 99.3% (29 minutes) of the time. It works how I want it, but is there any way to implement this in a faster manner?

test

(time,data)

AF1

index

AF1

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1 Answer
1

Memory permitting and barring one-off case when index ~= 1, you can use a vectorized approach with a family of useful functions that includes bsxfun and accumarray, well supported by find and abs, under the able guidance of linear indexing -

index ~= 1

bsxfun

accumarray

find

abs

linear indexing

[R,C] = find(abs(bsxfun(@minus,AF1(:,1),test(:,1).')) < 10^-6) %//'
idx = accumarray(R,C,,@max)

AF1((index-1)*size(AF1,1) + find(idx)) = test(idx(idx~=0),2);


Memory not permitting, thou shalt commit the crime of using a loop, that would be a modified version of the existing loop, like so -

valid_mask = true(size(AF1,1),1);
for a = size(test,1):-1:1
aaa = (abs(AF1(:,1)-test(a,1))<comp_val) & valid_mask;
valid_mask(aaa) = 0;
AF1(aaa,index)=test(a,2);
end