CODEWITHSUNDEEP
matlabmatrixfrequency
user8162
user8162

Reputation: 221

find the numbers that are NOT most frequent from a matrix in matlab

I would like to find the numbers that are not most frequent from a matrix for every column in matlab

for eg..,

 a = [3 3 1 4; 0 0 1 1; 0 1 2 4]

The answer I expect is 

[3 3 2 1]

Any help would be greatly appreciated.

Thanks in advance.

Regards,

Raja

Upvotes: 3

Views: 71

Answers (2)

Divakar
Divakar

Reputation: 221544

Assuming that in case of a tie for the minimum count in a column, you would settle for the minimum valued element, this is a bsxfun based solution code to solve it -

%%// Unique values across the entire matrix
unqval = unique(a(:))

%// Counts of those unique values for each column
counts = sum(bsxfun(@eq,a,permute(unqval,[3 2 1])),1)

%// Make the zero counts as NaNs as they don't exist at all for a column
counts(counts==0)=NaN

%// Indices for the minimum counts with the minimum valued element in a tie-case
[~,v2] = nanmin(permute(counts,[3 2 1]))

%// Minimum count elements of input for each coloumn, to form the desired output
out = unqval(v2).'

Alternative approach using for-loop -

alf(1,size(a,2))=0; %// alf would be the desired output
for k = 1:size(a,2)
    unqval = unique(a(:,k));
    [~,ind] = min(histc(a(:,k),unqval));
    alf(k) = unqval(ind);
end

Upvotes: 2

Luis Mendo
Luis Mendo

Reputation: 112659

This gives the lowest value in case of a tie:

u = unique(a(:)).'; %'// find unique values of a
h = histc(a, u); %// count for each value, in each column
h(h==0) = inf; %// mark non-present values
[~, r] = min(h); %// find first (i.e. lowest) value with minimum count
result = u(r); %// build result

Upvotes: 1

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