Store sets of values as indices in a matrix?

Hi,

I have a function which produces a set of horizontal and vertical graph axes intercepts. There are 120 sets of these intercepts:

for Z = 1:120

hrz = hix(x(:,Z),mb(:,Z))'; %[X Y] Matrix of horizontal intercepts

vrt = vix(y(:,Z),mb(:,Z))'; %[X Y] Matrix of vertical intercepts

end

I want to store each of these sets of intercepts in a matrix, i.e. I want to be able to call the second set of intercepts by simply calling matrix(2).

Is anyone aware of a way to achieve this?

Thanks

Answer 1

[Guillaume]

I'm assuming that hix and vix are functions, and I'm assuming that for each pair of vector input, they each return a vector of the same size as the input. In which case,

hrz = zeros(size(x));   %predeclare output matrix
vrt = zeros(size(x));
for Z = 1:120
   hrz(:, Z) = hix(x(:, Z), mb(:, Z));
   vrt(:, Z) = vix(y(:, Z), mb(:, Z));
end

[BOB]

Hi yes they are each functions.

This solution does not seem to work? The function produces a set of intercepts (one for each input of 1:120). I want to store all of these sets produced from loop in one matrix i.e. a matrix with 120 indices, each of these indices corresponds to a set of intercepts.

Apologies if my initial question was not too clear.

[Guillaume]

In what way does it not work? It errors? (if so which error), it produces something different than expected (if so what does it produce and what was expected?)

Are all the assumption that I've made correct? In particular, if you change the loop to

for Z = 1:120
   temp = hix(x(:, Z), mb(:, Z));
   assert(numel(temp) == size(x, 1), 'assumption broken');
   hrz(:, Z) = temp;
   vrt(:, Z) = vix(y(:, Z), mb(:, Z));
end

does it show assumption broken?

[BOB]

No it doesn't. I think I've been trying to ask the wrong question. What I want to do is store the (different length) vector of each iteration of the loop in a single matrix. Is this possible through some clever tricks?

[BOB]

And the error returned is "Assignment has more non-singleton rhs dimensions than non-singleton subscripts"

[Guillaume]

store the different length vector of each iteration of the loop in a single matrix.

Ah! That needed explaining in the question. By definition, a matrix has the same number of rows/columns for each column/row. So you can't store results of varying length in a matrix unless you pad the shorter ones (which is rarely a good approach).

You can store the results in a cell array though:

hrz = cell(1, size(x, 2));   %preallocate output
vrt = cell(1, size(x, 2));  
for Z = 1:size(x, 2)   %better not to hardcode the size
  hrz{Z} = hix(x(:, Z), mb(:, Z));
  vrt{Z} = vix(y(:, Z), mb(:, Z));
end

[BOB]

That works perfectly! Thanks for the persistence, I'll make sure to be more clear next time.