Generate combinations of Cells that contain text

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Andreas Georgakakos
评论： Guillaume 2019-5-24
Hi there,
I am trying to generate all the combinations of certain cells so that each combination will include only one element of each vector/category. For example:
A = {'Square'; 'Rectangle'}
B = {'Heavy'; 'Light'; 'Medium'}
C = {'West'; 'East', 'South'; 'North'}
For output, I want a matrix that will have the following structure:
D = { 'Square-Heavy-West'; 'Square-Heavy-East' etc.}
If this would be possible without using cells, I would appreciate your thoughts.
Thank you in advance,
Andreas
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Andreas Georgakakos
Andreas Georgakakos 2018-4-4
I am open to using cells as well, just wondering if there is an alternative. But as I said, cells are fine too.
Stephen23
Stephen23 2019-5-21
"...but I don't believe it is possible to make an array of strings without doing cells, structures, or a table"
String arrays were introduced in R2016b. These are by definition an array of strings.

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回答（3 个）

Stephen23
Stephen23 2019-5-21
编辑：Stephen23 2019-5-21
Simple and efficient with ndgrid and strcat:
>> [Cx,Bx,Ax] = ndgrid(1:numel(C),1:numel(B),1:numel(A));
>> D = strcat(A(Ax(:)),'-',B(Bx(:)),'-',C(Cx(:)))
D =
'Square-Heavy-West'
'Square-Heavy-East'
'Square-Heavy-South'
'Square-Heavy-North'
'Square-Light-West'
'Square-Light-East'
'Square-Light-South'
'Square-Light-North'
'Square-Medium-West'
'Square-Medium-East'
'Square-Medium-South'
'Square-Medium-North'
'Rectangle-Heavy-West'
'Rectangle-Heavy-East'
'Rectangle-Heavy-South'
'Rectangle-Heavy-North'
'Rectangle-Light-West'
'Rectangle-Light-East'
'Rectangle-Light-South'
'Rectangle-Light-North'
'Rectangle-Medium-West'
'Rectangle-Medium-East'
'Rectangle-Medium-South'
'Rectangle-Medium-North'
"If this would be possible without using cells, I would appreciate your thoughts."
You could use string arrays, but the methods to generate all combinations would be exactly the same.
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Rik
Rik 2019-5-24
RE: strfind, that is one of the examples where Octave sticks to the documented behavior, as it throws an error on numeric input. I know this question is not related to Octave, but I just wanted to put it out there.
Guillaume
Guillaume 2019-5-24
I've always felt a bit ambivalent about the fact that strfind can find sequences in numeric arrays. It is very handy (and you'll find it suggested every now and then on Answers) but a function with such a name shouldn't deal with numbers.
The best thing would be to either change the name (FindSequence) or simply duplicate the function with a new name that clearly applies to numerics.

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Fabian Torres
Fabian Torres 2019-5-21
This worked for me but I am not sure about how fast can it be compared with the loop, but still more elegant:
A = {'Square'; 'Rectangle'}; nA = size(A, 1);
B = {'Heavy'; 'Light'; 'Medium'}; nB = size(B, 1);
C = {'West'; 'East'; 'South'; 'North'}; nC = size(C, 1);
D = reshape(strcat(repmat(B, 1, nC), '-', repmat(C', nB, 1))', [], 1);
nD = size(D, 1);
D = reshape(strcat(repmat(A, 1, nD), '-', repmat(D', nA, 1))', [], 1);
Bob Thompson
Bob Thompson 2018-4-4
If somebody knows a way to conduct this without loops feel free to mention it, but I do know that you can record all possible combinations using a set of for loops. Indexing can be a pain though if you just want a series of rows. Easier to look at as an output, just tricky to code.
lenA = size(A,1);
lenB = size(B,1);
lenC = size(C,1);
for first = 1:lenA; % Loop through first matrix
for second = 1:lenB; % Loop through second matrix
for third = 1:lenC; % Loop through third matrix
D{(first-1)*lenB*lenC+(second-1)*lenC+third,1} = A{first}; % Record word from first
D{(first-1)*lenB*lenC+(second-1)*lenC+third,2} = B{second}; % Record word from second
D{(first-1)*lenB*lenC+(second-1)*lenC+third,3} = C{third}; % Record word from third
% End single combination
end
end
end

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