Number of rows based on frequency of one integer and position of another integer

2 views (last 30 days)
Hello. I was wondering if someone could help me with this:
Let's say you have a 2000 x 2 matrix, where all the elements are integers. How can we count the number of rows that contain the number 10 in its first column and any number with the highest 5 integers in the second column?
In other words, the following but where X is the fifth highest number in the second column:
nnz(matrix(:,1) == 10 & matrix(:,2) > X);
EDIT -> Very importantly, the list with the highest 5 integers must be determined for each integer in the first column. So, if one wanted to do this for the number 10, it must be determining the highest 5 integers in the second column WHEN the integer in the first column is 10.
Thanks!

Accepted Answer

Voss
Voss on 17 Jan 2022
Get the set of unique numbers in the 2nd column:
col2_vals = unique(matrix(:,2));
The 5th highest is 4th from the end. So, to match any number within the highest 5:
nnz(matrix(:,1) == 10 & matrix(:,2) >= col2_vals(end-4));
  4 Comments
Voss
Voss on 18 Jan 2022
idx = matrix(:,1) == 10;
col2_vals = unique(matrix(idx,2)); % now: unique values of column 2 where column 1 is 10
nnz(matrix(idx,2) >= col2_vals(end-4));

Sign in to comment.

More Answers (1)

David Hill
David Hill on 17 Jan 2022
r=unique(matrix(:,2));
r=r(end-4:end);
n=nnz(matrix(:,1)==10&ismember(matrix(:,2),r));
  3 Comments
David Hill
David Hill on 18 Jan 2022
r=unique(matrix(matrix(:,1)==10,2));
r=r(end-4:end);
n=nnz(matrix(:,1)==10&ismember(matrix(:,2),r));
Neuro
Neuro on 18 Jan 2022
Thanks @David Hill, but it gives me an error message:
Error using unique (line 117)
Invalid input. Valid flags are 'rows', 'first', 'last', 'stable', 'sorted', 'legacy'.

Sign in to comment.

Products


Release

R2021b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!