comparing rows of a logical matrix in matlab? - matlab

Question

I have sentences cross words [4 cross 5] matrix as follows:
out=
0 1 1 0 1
1 1 1 0 0
0 0 1 1 0
1 1 0 1 1
I want to create a 1D cell array based upon above matrix which should tell in which two sentences same words appear with value = 1 i.e. let's take line 1 and line 2 in which at 2 points column 2 and column 3 the logical matrix has both 1's in row 1 and row 2 this information should be stored in 1D cell array.
suppose above example it's output would be as:
output{1,1} = []
output{1,2} = [2 3]
output{1,3} = [3]
.....
output{n,n} = [....]
where {1,1} tells sentence 1 relation with sentence 1 on the basis of value=1 of words, {1,2} tells sentence 1 relation with sentence 2 on the basis of value=1 of words and so on...

Answer 1

Try this:
x = [ 0 1 1 0 1
1 1 1 0 0
0 0 1 1 0
1 1 0 1 1];
[ii, jj] = ndgrid(1:size(x,1));
y = arrayfun(#(m,n) find(x(m,:) & x(n,:)), ii, jj, 'uniformoutput', 0);
Result:
y{1,1} =
2 3 5
y{2,1} =
2 3
y{3,1} =
3
y{4,1} =
2 5
[...]
If you want the diagonal elements to be empty:
y = arrayfun(#(m,n) find(x(m,:) & x(n,:) & m~=n), ii, jj, 'uniformoutput', 0)
Result:
y{1,1} =
[]
y{2,1} =
2 3
y{3,1} =
3
y{4,1} =
2 5
[...]

Answer 2

If you want something written quick... and since we are dealing with cell arrays, the easiest thing would be to have a pair of for loops. Assuming that you have your matrix defined in out:
out_cell = cell(size(out,1),size(out,1));
for idx = 1 : size(out,1)
for idx2 = 1 : idx
vals = find(out(idx,:) & out(idx2,:));
out_cell{idx,idx2} = vals;
out_cell{idx2,idx} = vals;
end
end
For each pair of rows, idx and idx2, we look to see if any columns match in terms of having a 1, then place the indices into its respective cell location in the 2D cell array. Note that because will encounter pairs of rows that are duplicates (i.e. checking row 3 and row 5, compared to row 5 and row 3), there is no need for the second for loop to iterate all over the other rows. We only need to check up to the current row that is described by the outer loop and we simply write the same values with the row indices swapped... so this is a "symmetric" matrix.
If you would like the diagonal elements to be empty, simply change the inner for loop so that it goes for idx2 = 1 : idx-1, instead of for idx2 = 1 : idx.
With your example, we get:
>> out_cell
out_cell =
[1x3 double] [1x2 double] [ 3] [1x2 double]
[1x2 double] [1x3 double] [ 3] [1x2 double]
[ 3] [ 3] [1x2 double] [ 4]
[1x2 double] [1x2 double] [ 4] [1x4 double]
>> celldisp(out_cell)
out_cell{1,1} =
2 3 5
out_cell{2,1} =
2 3
out_cell{3,1} =
3
out_cell{4,1} =
2 5
out_cell{1,2} =
2 3
out_cell{2,2} =
1 2 3
out_cell{3,2} =
3
out_cell{4,2} =
1 2
out_cell{1,3} =
3
out_cell{2,3} =
3
out_cell{3,3} =
3 4
out_cell{4,3} =
4
out_cell{1,4} =
2 5
out_cell{2,4} =
1 2
out_cell{3,4} =
4
out_cell{4,4} =
1 2 4 5