cell comparison with other cells in different rows
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I have a 6x2 cell array. Each cell is a 1x2 cell that contains an x and y co-ordinate. I want to be able to compare the contents of each cell of every row with the contents of each cell of the other rows. Each row of the cell array stands for a line. Essentially what I need to do is to determine which rows are connected together by finding the common endpoint.
I saw something on here that I think I can utilize. It's called nchoosek. This function basically finds all possible rows combination's for a give size. The following code uses this function. The problem that I am having is that I get all zero's for the keys.
endpoints = {{-24.7697910000000,-15.8191235000000},{-20.6771670000000,-3.54125200000000};{-12.6771670000000,20.4587480000000},{-20.6771670000000,-3.54125200000000};{-11.9803417500000,-14.5401785500000},{13.0196582500000,-12.0401785500000};{-11.9803417500000,-14.5401785500000},{-24.7697910000000,-15.8191235000000};{4.32283300000000,-1.04125200000000},{-12.6771670000000,20.4587480000000};{4.32283300000000,-1.04125200000000},{13.0196582500000,-12.0401785500000}};
comparisons = nchoosek(1:size(endpoints,1),2);
N = size(comparisons,1);
keys = cell(N,1);
for j = 1:N
keys{j}=isequal(endpoints{comparisons(j,1),:},endpoints{comparisons(j,2),:});
end
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Richard Brown
il 12 Apr 2012
For the record, it would be better to use arrays rather than cell arrays for the coordinates (in fact for the whole thing, but that's ok).
Anyway, this should do the trick:
ep = {{-24.7697910000000,-15.8191235000000},{-20.6771670000000,-3.54125200000000};
{-12.6771670000000,20.4587480000000},{-20.6771670000000,-3.54125200000000};
{-11.9803417500000,-14.5401785500000},{13.0196582500000,-12.0401785500000};
{-11.9803417500000,-14.5401785500000},{-24.7697910000000,-15.8191235000000};
{4.32283300000000,-1.04125200000000},{-12.6771670000000,20.4587480000000};
{4.32283300000000,-1.04125200000000},{13.0196582500000,-12.0401785500000}};
n = size(ep, 1);
V = nchoosek(1:n, 2);
key = false(n, 1);
% Convert the points to vectors
ep = cellfun(@(x) cell2mat(x), ep, 'UniformOutput', false);
is_same = @(x, y) norm(x - y, inf) / norm(x, inf) < 100*eps;
for i = 1:size(V, 1)
% Do the four comparisons
i1 = V(i,1);
i2 = V(i,2);
key(i) = is_same(ep{i1, 1}, ep{i2, 1}) || ...
is_same(ep{i1, 1}, ep{i2, 2}) || ...
is_same(ep{i1, 2}, ep{i2, 2}) || ...
is_same(ep{i1, 2}, ep{i2, 2});
end
matches = V(key, :);
3 Commenti
Richard Brown
il 12 Apr 2012
It's pretty simple - the only particularly obfuscated line is the cellfun one - it just converts all of the points into arrays rather than cell arrays (so you can add, subtract, take norms, etc), while keeping the overall cell array structure.
The is_same line is a convenient anonymous function for comparing two vectors - basically just saves a whole lot of typing, given that you need to compare four different pairs each pass through the main loop.
Più risposte (1)
Andrei Bobrov
il 11 Apr 2012
[EDIT] :)
ep = {{-24.7697910000000,-15.8191235000000},{-20.6771670000000,-3.54125200000000};
{-12.6771670000000,20.4587480000000},{-20.6771670000000,-3.54125200000000};
{-11.9803417500000,-14.5401785500000},{13.0196582500000,-12.0401785500000};
{-11.9803417500000,-14.5401785500000},{-24.7697910000000,-15.8191235000000};
{4.32283300000000,-1.04125200000000},{-12.6771670000000,20.4587480000000};
{4.32283300000000,-1.04125200000000},{13.0196582500000,-12.0401785500000}};
M = cell2mat(cellfun(@(x)cell2mat(x),ep,'un',0));
cmb = nchoosek(1:size(M,1),2);
ic = arrayfun(@(i1)any(ismember(M(cmb(i1,1),:),M(cmb(i1,2),:))),(1:size(cmb,1))');
pout = cmb(ic,:);
4 Commenti
Richard Brown
il 11 Apr 2012
If you're only calling nchoosek with k of 2, you can go much higher than 15. The number of possible combinations is just n*(n-1)/2. And if nchoosek is too slow (once you get into the thousands), then you can easily do it with two nested loops.
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