Speed up for loop, accumarray
显示 更早的评论
I would like to speed up my two for loop with accumarray (I have old version of MatLab and I've read on internet that accumarray will speed up my operation)
if true
for i = 1:size(img, 1)
for j = 1:size(img, 2)
R = idx(i, j, 1);
G = idx(i, j, 2);
B = idx(i, j, 3);
H(R,G,B) = H(R,G,B) + 1;
end
end
end
采纳的回答
This gives exactly the same output as your code:
H = accumarray(reshape(idx,[],3),1);
First I ran your code on some random arrays:
img = randi(6,5,4,3);
idx = img;
H = zeros(6,6,6);
for i = 1:size(img, 1)
for j = 1:size(img, 2)
R = idx(i, j, 1);
G = idx(i, j, 2);
B = idx(i, j, 3);
H(R,G,B) = H(R,G,B) + 1;
end
end
Then compared the outputs:
>> Z = accumarray(reshape(idx,[],3),1);
>> isequal(Z,H)
ans = 1
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