MATLAB: How to use a for loop for concatenated matrices. [counts, centers] = hist(X);

.binbin centersconcatenatefor loophisthistogramhistogram bin countsmatrix manipulation

Hello Friends,
I am trying to do the following:
[counts1, centers1] = hist(X); [counts2, centers2] = hist(Y);
%X and Y both are the n x 1 matrices, i.e., have only one column with real numbers.
counters = [counts1, centers1; counts2, centers2]; %Here, I am trying to make a 2x2 matrix.
Now, I want to compute the expected value as follows:
[row, col] = size(counters);
E = zeros(row);
for i = 1:row
    E(i) = (counters(i,1)*counters(i,2)')/sum(counters(i,1));
    fprintf('%f\n', E(i)); % Trying to print it on command window.
end
I am not getting expected results. Expected Values E(1) and E(2) should print on command window separately for each sets of counts & centers (let's say we want to print them in column). Please advise. Thanks in advance.

Best Answer

hello_world - counters is more likely a 2x20 matrix as counts1, counts2, centers1, and centers2 are (probably) 1x10 matrices since the default number of bins when using hist is 10. If that is the case, and you want to determine the expectation of X and Y, then I suspect that you have to make use of all of the column data.
Try saving the data to a cell array so that you can maintain the 2x2 matrix (that you originally hoped for)
 counters = {counts1, centers1; counts2, centers2};
Now calculate the expectation as
 [row, col] = size(counters); 
 E = zeros(row);
 for k = 1:row
    E(i) = sum(counters{k,1}.*counters{i,2})/sum(counters{i,1});
    fprintf('%f\n', E(i)); % Trying to print it on command window.
 end
For each row, we do
 E(i) = sum(counters{k,1}.*counters{i,2})/sum(counters{i,1});
where, for each of the ten bins, we multiply the bin count by the bin centre. We sum these values and divide by the sum of all bin counts to get the expectation.
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