2d matrix histogram in matlab that interprets each column as a separate element

Question

I have a 128 x 100 matrix in matlab, where each column should be treated as a separate element. Lets call this matrix M.

I have another 128 x 2000 matrix(called V) composed of columns from matrix M.

How would I make a histogram that maps the frequency of each column being used in the second matrix?

hist(double(V),double(M)) gives the error:

 Error using histc
Edge vector must be monotonically
non-decreasing.

what should I be doing?

Amro Amro · Accepted Answer · 2012-06-21T06:20:51

Here is an example. We start with data that resembles what you described

%# a matrix of 100 columns
M = rand(128,100);
sz = size(M);

%# a matrix composed of randomly selected columns of M (with replacement)
V = M(:,randi([1 sz(2)],[1 2000]));

Then:

%# map the columns to indices starting at 1
[~,~,idx] = unique([M,V]', 'rows', 'stable');
idx = idx(sz(2)+1:end);

%# count how many times each column occurs
count = histc(idx, 1:sz(2));

%# plot histogram
bar(1:sz(2), count, 'histc')
xlabel('column index'), ylabel('frequency')
set(gca, 'XLim',[1 sz(2)])

enter image description here

2d matrix histogram in matlab that interprets each column as a separate element

2 Answers