how to calculate number of unique element in array?

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Putri Basenda Tarigan
评论： Putri Basenda Tarigan 2020-11-22
Hi all.
if I have matrix like:
c =
1 1
1 1
1 1
2 1
2 2
2 3
2 4
2 5
2 5
3 1
3 1
3 2
how can I calculate number of unique element in column 2 according to column 1?
for the above matrix, the result should be:
1 1
2 5
3 2
Thanks in advance

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采纳的回答

Ameer Hamza
Ameer Hamza 2020-11-22
编辑：Ameer Hamza 2020-11-22
Try splitapply()
c = [
1 1
1 1
1 1
2 1
2 2
2 3
2 4
2 5
2 5
3 1
3 1
3 2]
out = [unique(c(:,1)) ...
splitapply(@(x) numel(unique(x)), c(:,2), c(:,1))]
or accumarray():
out = [unique(c(:,1)) ...
accumarray(c(:,1), c(:,2), [], @(x) numel(unique(x)))];
And if the second column also contain all positive integers in increasing order then you can just try
out = [unique(c(:,1)) ...
splitapply(@max, c(:,2), c(:,1))]
%
out = [unique(c(:,1)) ...
accumarray(c(:,1), c(:,2), [], @max)];

更多回答（1 个）

Bruno Luong
Bruno Luong 2020-11-22
编辑：Bruno Luong 2020-11-22
c =[
1 1
1 1
1 1
2 1
2 2
2 3
2 4
2 5
2 5
3 1
3 1
3 2 ]
d=unique(c,'rows');
c1=d(:,1);
i=find([true; diff(c1)~=0; true]);
count=diff(i);
c1=c1(i(1:end-1));
t=table(c1,count)

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