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From: Namo Namo on 16 Jul 2010 14:17
Say I have a matrix

a = [ 1 2 2
2 3 3
1 4 5 ];

I want to count the occurences of 1 2 ... 5, but by how many rows. That is, although 2 appears 3 times, but only in 2 rows. I can count the total times by tabulate(a(:)) or histc, accumarray, etc. But to count the total rows, I am doing a for loop

for i = 1:N
count(i) = sum( any( a==i, 2) )
end

any advice on how to speep up for large N? Thanks.
From: us on 16 Jul 2010 14:45
"Namo Namo" <wynamo(a)yahoo.com> wrote in message <i1q7ng$78g$1(a)fred.mathworks.com>...
> Say I have a matrix
>
> a = [ 1 2 2
> 2 3 3
> 1 4 5 ];
>
> I want to count the occurences of 1 2 ... 5, but by how many rows. That is, although 2 appears 3 times, but only in 2 rows. I can count the total times by tabulate(a(:)) or histc, accumarray, etc. But to count the total rows, I am doing a for loop
>
> for i = 1:N
> count(i) = sum( any( a==i, 2) )
> end
>
> any advice on how to speep up for large N? Thanks.

one of the solutions

% the data
a=[
1 2 2
2 3 3
1 4 5
];
% the engine
nx=1:max(a(:));
n=histc(a.',nx);
n=sum(n~=0,2);
% the result
disp([nx;n.']);
%{
1 2 3 4 5 % <= unique val...
2 2 1 1 1 % <- #rows
%}

us
From: Sean on 16 Jul 2010 15:09
"Namo Namo" <wynamo(a)yahoo.com> wrote in message <i1q7ng$78g$1(a)fred.mathworks.com>...
> Say I have a matrix
>
> a = [ 1 2 2
> 2 3 3
> 1 4 5 ];
>
> I want to count the occurences of 1 2 ... 5, but by how many rows. That is, although 2 appears 3 times, but only in 2 rows. I can count the total times by tabulate(a(:)) or histc, accumarray, etc. But to count the total rows, I am doing a for loop
>
> for i = 1:N
> count(i) = sum( any( a==i, 2) )
> end
>
> any advice on how to speep up for large N? Thanks.

Another solution:

A = [2 3 2; 4 2 5; 1 3 7];
Acell = cellfun(@unique,mat2cell(A,ones(1,3),3),'UniformOutput',false);
U = unique(A);
[n] = histc(cell2mat(Acell'),U);
table = [U, n'] %U is the value n is the occurance
From: Namo Namo on 16 Jul 2010 15:13

> > Say I have a matrix
> >
> > a = [ 1 2 2
> > 2 3 3
> > 1 4 5 ];
> >
> > I want to count the occurences of 1 2 ... 5, but by how many rows. That is, although 2 appears 3 times, but only in 2 rows. I can count the total times by tabulate(a(:)) or histc, accumarray, etc. But to count the total rows, I am doing a for loop
> >
> > for i = 1:N
> > count(i) = sum( any( a==i, 2) )
> > end
> >
> > any advice on how to speep up for large N? Thanks.
>
> one of the solutions
>
> % the data
> a=[
> 1 2 2
> 2 3 3
> 1 4 5
> ];
> % the engine
> nx=1:max(a(:));
> n=histc(a.',nx);
> n=sum(n~=0,2);
> % the result
> disp([nx;n.']);
> %{
> 1 2 3 4 5 % <= unique val...
> 2 2 1 1 1 % <- #rows
> %}
>
> us


I actually used this before. It becomes slow for me because for me, a is like 1e5 rows and 5 columns, and max(a(:)) = 4000. So it takes a long time and generates a large n when I perform histc for each row of a, each time sorting 5 numbers into 4000 bins :-(. Thanks anyway.
From: Bruno Luong on 16 Jul 2010 15:18
Another solution:

a=[1 2 2;
2 3 3;
1 4 5];

sum(accumarray([mod((0:numel(a)-1)',size(a,1))+1 a(:)],1)>0)

Bruno
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