Code optimization by avoiding loops
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I have the following Data and Variables
data = 1000x2 double array containing x and y coordinates
B = 1000x1 integer array containing category values from 1 to j inclusive
A = need to create this array which contains values that are the mean of all the points for each category (x and y values to be averaged separately)
I have the following code which works as desired. I am wondering whether there is a better way of doing it without the loop,
for i = 1:j
A(i,:) = mean(data(B==i,:));
end
Thank you.
采纳的回答
B=B(:);
N=accumaray(B,1);
A(:,1)=accumaray(B,data(:,1))./N;
A(:,2)=accumaray(B,data(:,2))./N;
6 个评论
Matt J
2017-12-2
You could also use accumarray(...,@mean) but in past Matlab versions, at least, that has been found to be slower.
Alex
2017-12-2
Can you please suggest the full code out of interest?
A(:,1)=accumaray(B(:),data(:,1),[],@mean);
A(:,2)=accumaray(B(:),data(:,2),[],@mean);
I'm new to matlab and not familiar with that expression?
Since you're new, it will benefit you to know that you can bring up usage documentation on any command, e.g.,
>> doc accumarray
Alex
2017-12-2
Matt J
2017-12-2
A fancy trick you might be able to do is
args=[accumarray(B(:),data(:,1),[],@(q) {q}),...
accumarray(B(:),data(:,2),[],@(q) {q})].';
plot(args{:})
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