Search particular matrix in cell array

Question

So, I have this cell array contains n x 2 matrix in each cell. Here is the sample data :

[16 17;17 17]
<6x2 double>
<52x2 double>
[17 17;17 18]
[17 18;17 17]

What I am going to do is eliminate the duplicated matrix (matrices with same values or reversed values). in this case is [17 18; 17 17] (5th row), because we already have [17 17; 17 18] (4th row)

I tried using unique function but it says that the function just worked for strings. I also tried to find it with cellfun like this

cellfun(@(x) x==whatToSearch, lineTraced, 'UniformOutput', false)

but it says 'Matrix dimension must agree'

Thanks in advance.

So if two matrices A and B are equal, they are still equivalent after some arbitrary permutation of rows? — eigenchris
No, A and B considered equal if A is a 'mirrored' version of B vice versa (e.g if A=[1 2 3 4 5] and B=[5 4 3 2 1], A and B is considered equal). Thanks for noticing this, I'll update my question. — Abdullah Al Mubarok
If mirrored or flipped, is it upside down flipped or left-right flipped? It appears to be upside-down flipped to me. — Divakar
Let me revise my previous example to make it clear. If A=[1 2; 3 4; 5 6] and B=[5 6; 3 4; 1 2], A and B is considered equal — Abdullah Al Mubarok

Sevenless Sevenless · Accepted Answer · 2015-03-10T19:06:58

Here's code that does what you want.

mydup = rand(5,2);
mycell = {mydup;mydup;rand(7,2);rand(3,2);rand(5,2)}

myNewCell = trimCell(mycell)

Where trimCell is the function below:

function myNewCell = trimCell(myCell)


exclude = false(size(myCell));
for iter = 1:size(myCell,1)
    toCompare = myCell{iter};
    comparisons = cellfun(@(x) all(size(x)==size(toCompare)) && myEquals(x, toCompare),myCell);
    % comparisons has at least 1 true in it, because toCompare==toCompare
    exclude(iter) = sum(comparisons)>1;
end

myNewCell = myCell(~exclude);

end

function boolValue = myEquals(x,y)

assert(all(size(x)==size(y)));

boolValue = true;
for iter = 1:size(x,1)
    thisRow = all(sort(x(iter,:))==sort(y(iter,:)));
    boolValue = boolValue && thisRow;
    if ~boolValue
       return 
    end

end

end

Basically, what this function does, is, for each matrix in the cell it checks first if the sizes are equal. If the sizes aren't equal, then we know the matrices aren't equal, even if we reorder the rows.

If they are the same size, then we need to check if they're equal after row reordering. That's accomplished by the function myEquals which goes through row by row and sorts the rows before comparing them. It exits with false on the first row it finds that is not equal after reordering.

Hope this helps, Andrew

Search particular matrix in cell array

2 Answers