CODEWITHSUNDEEP
arraysmatlab
MikiBelavista
MikiBelavista

Reputation: 2728

Count occurrence of array elements

Well I have an array called A:

[8 2
6 1
6 1
6 1
1 2]

How to count the occurrence of the same rows? It does not work well with unique because it does not differentiate between the rows.

Upvotes: 1

Views: 108

Answers (3)

Divakar
Divakar

Reputation: 221564

One bsxfun+unique approach -

binmat1 = squeeze(all(bsxfun(@eq,A,permute(A,[3 2 1])),2))
[~,ind1] = unique(bi2de(binmat1),'stable')
uniqueA = A(ind1,:)
counts = sum(binmat1(ind1,:),2)

Thus, if you have A as:

A=[ 8 2;
    6 1;
    6 1;
    6 1;
    1 2;
    63 1;
    63 1]

Output would be:

uniqueA =
     8     2
     6     1
     1     2
    63     1

counts =
     1
     3
     1
     2

Upvotes: 0

Luis Mendo
Luis Mendo

Reputation: 112669

sparse approach:

>> sparse(A(:,1), A(:,2), 1)
ans =
   (6,1)        3
   (1,2)        1
   (8,2)        1

If you need it in the form of two variables as in Daniel's answer:

[ii jj Occurrences] = find(sparse(A(:,1), A(:,2), 1));
Rows = [ii jj];

which gives

Rows =
     6     1
     1     2
     8     2

Occurrences =
     3
     1
     1

Upvotes: 3

Daniel
Daniel

Reputation: 36710

Use unique to get the indices.

[R,ixb,ix]=unique(A,'rows')

Then use histc to count them

O=histc(ix,1:numel(ixb))

R contains the (unique) rows and O the number of occurrences.

Upvotes: 1

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