How can I randomly select words from a column without replacement?

I'd like to use a cell array to make 3 random sentences with no repeated words (using MATLAB 2018b):

myarray = {'John' 'likes' 'cats'; 'Alex' 'hates' 'rabbits'; 'Lucy' 'loves' 'frogs'};
Column1 = myarray(:,1);
Column2 = myarray(:,2);
Column3 = myarray(:,3);

for n = 1:3
Word1 = Column1(randperm(length(Column1),1));
Word2 = Column2(randperm(length(Column2),1));
Word3 = Column3(randperm(length(Column3),1));
n = [Word1 Word2 Word3]
end

but I often get repeated words, like this:

{'John'}    {'loves'}    {'rabbits'}
{'John'}    {'likes'}    {'rabbits'}
{'Lucy'}    {'likes'}    {'frogs'}

How can I make it so that all words are used and no words are repeated? Thanks in advance.

Answer 1

[Image Analyst]

You can get the random numbers in advance of your loop, then simply use them. It's also very bad practice to redefine your loop iterator, n, inside your loop. See improved code below:

myarray = {'John' 'likes' 'cats'; 'Alex' 'hates' 'rabbits'; 'Lucy' 'loves' 'frogs'};
Column1 = myarray(:,1);
Column2 = myarray(:,2);
Column3 = myarray(:,3);
% Get random numbers, not repeating.
r1 = randperm(3);
r2 = randperm(3);
r3 = randperm(3);
for n = 1:3
  Word1 = Column1{r1(n)};
  Word2 = Column2{r2(n)};
  Word3 = Column3{r3(n)};
%   n = [Word1 Word2 Word3]  % DON'T DO THIS!
  fprintf('%s %s %s\n', Word1, Word2, Word3);
end

[Sarah]

Many thanks for the improved code and the tip to not redefine n inside the loop! I also realized, in working through your suggestion, that I can add an array, S:

myarray = {'John' 'likes' 'cats'; 'Alex' 'hates' 'rabbits'; 'Lucy' 'loves' 'frogs'};
Column1 = myarray(:,1);
Column2 = myarray(:,2);
Column3 = myarray(:,3);
r1 = randperm(3);
r2 = randperm(3);
r3 = randperm(3);
S = {};
for n = 1:3
Word1 = Column1{r1(n)};
Word2 = Column2{r2(n)};
Word3 = Column3{r2(n)};
S(n,:) = {Word1 Word2 Word3};
end

...which gives me a nice output array:

{'John'}    {'likes'}    {'cats'}
{'John'}    {'loves'}    {'frogs'}
{'Lucy'}    {'likes'}    {'cats'}

...which (though I completely neglected to mention this in the original question) is what I ultimately needed.

Anyway, thank you again!

Answer 2

[Guillaume]

Use randperm properly. randperm(x, 1) is the same as randi(x) and of course if you do that 3 times, there's no guarantee you don't get repetition. randperm(x, 3) guarantees you to pick 3 different random numbers. And since your array has only 3 rows, randperm(x) would work just as well:

p = zeros(size(myarray));
for col = 1:size(myarray, 2)
  p(:, col) = randperm(size(myarray, 2)) + (col-1) * size(myarray, 1);
end
result = myarray(p)

[Sarah]

Thank you! This also works well.