How to calculate repetition of an unknown number present in 2nd column of a 150*2 matrix?

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I've a matrix a=[1,1;2,1;3,1;4,4;5,4] . Actually numbers in the 2nd column are not known in a general case. So, how can i count how many numbers have a particular number (say 1,4) in their corresponding 2nd column.

Accepted Answer

Star Strider
Star Strider on 20 May 2016
Use the unique and accumarray functions:
[a2,ia,ic] = unique(a(:,2));
ah = accumarray(ic, 1);
Result = [a2, ah]
Result =
1 3
4 2
So in the second column, there are 3 ‘1’ values and 2 ‘4’ values.
This could be easily changed if you wanted unique row pairs.

More Answers (1)

Alessandro Masullo
Alessandro Masullo on 20 May 2016
You can use the function hist (or histc) on the second column of your matrix.


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