Count number of times value appears in column

I have a 1000x296 matrix called FinalRanking. The possible values in each cell are between 1 and 296, integers.

I want to count the number of times each number, 1-296, appears in each column, and return this as a 296x296 matrix, lets call it counter.

so for example Counter(1,1) has the value of the number of time 1 appears in Column 1 of FinalRanking.

or Counter(12, 57) returns the value of the number of times 12 appears in Column 57 of FinalRanking.

How would I do this? I'm assuming i need nested for loops. Thanks!

Answer 1

[the cyclist]

% Parameterize the max value, for convenience
V = 296;

% Some simulated data
FinalRanking = randi(V,1000,V);

% Preallocate the counter array
counter = nan(V,V);

% Loop over the columns, and count the number of times each value appears
for nc = 1:V
    counter(:,nc) = histcounts(FinalRanking(:,nc),[1:V Inf]);
end

[Emma Kuttler]

This works perfectly, thank you!

Answer 2

[Andrei Bobrov]

out = histc(FinalRanking,1:296);

[the cyclist]

Emma, be aware that while histc is great because it can accept that entire matrix at once as an input, Mathworks recommends against using it (and presumably it could be removed in the future).

[Emma Kuttler]

Thanks, that's a really concise way to do it!

[Andrei Bobrov]

"If performance is a problem due to a large number of columns in the matrix, then consider continuing to use histc for the column-wise bin counts." - wrote The Mathworks.

[the cyclist]

Make up your mind, MathWorks! :-)

Answer 3

[Image Analyst]

Try this:

edges = 1 :  297;
FinalRanking = randi(296, 1000, 296);
counter = zeros(296, 296);
for col = 1 : size(FinalRanking, 2)
	counter(:, col) = histcounts(FinalRanking(:, col), edges);
end
imshow(counter, [], 'ColorMap', hsv(256));
axis('on', 'image');
colorbar;
impixelinfo;

[Emma Kuttler]

This is interesting! I'm guessing the x axis represents the column and y represents the number of occurences? If so, how do i modify the code to add axis labels?

[Image Analyst]

Yes for x. But along the y axis are the histogram bins. The value, "z" value if you want to think of it like that, is the count. But the actual distance/location along the y axis is the bin number, not the "number of occurrences" (counts).

fontSize = 20; % Whatever.
xlabel('Column', 'FontSize', fontSize);
ylabel('Number (i.e., histogram bin)', 'FontSize', fontSize);