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How do I replace same values in an array?

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Fabio
Fabio 2014-5-20
评论： Fabio 2014-5-22
If I have this couples of values: 1—5; 2—7; 3—4; 2—3; 6—5 and I want that the first column is the x column and the second one is the y column of an xy graph (especially an histogram), how can I make that for the same value of x, y is the sum of y values for the same x as follow? 1—5; 2—10; 3—4; 6—5.
Thank you
Fabio

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dpb
dpb 2014-5-20
If
xy=your array;
y=accumarray(xy(:,1),xy(:,2));
See
doc unique
doc accumarray
for how the above works...
>> xy=[1 5;2 4;3 8; 2 6];
>> [unique(xy(:,1)) accumarray(xy(:,1),xy(:,2))]
ans =
1 5
2 10
3 8
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dpb
dpb 2014-5-21
Or in place without a temporary,
ac(ac==0)=[]; % to delete zeros
You can also get more clever in using unique and accumarray together with the alternate outputs of unique as indices and anonymous functions to only sum the nonzero entities. I'll leave as "exercise for the student"; the nuances of accumarray are legion and an area of expertise to be gained all of its own. :)

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