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

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.

[KSSV]

How you can find out with out knowing the numbers?

Answer 1

[Star Strider]

Use the unique and accumarray functions:

a=[1,1;2,1;3,1;4,4;5,4];
[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.

[Binayak Gouda]

thank you ..

[Star Strider]

My pleasure!

Answer 2

[Alessandro Masullo]

You can use the function hist (or histc) on the second column of your matrix.