MATLAB: Change dimensions of a cell depending on the number of inputs

cell arraysvariable inputs

I am building a model with nodes made of different number of states. Each node is defined as a cell containing the probability of each state to happen. For example, the node A has 2 states and node B has 3 states, so they are represented as 1×2 and 1×3 cells, i.e.,

A = cell(1,2);

B = cell(1,3);

There is a third cell C that is a child node of A and B (i.e., probabilities of C are conditioned to those of A and B, the "parent nodes") that has 4 states. So, this will be a 2x3x4 cell, as follows:

C = cell(2,3,4);

Is there a Matlab function or a way to create automatically the cell C with dimensions that depend on the number of the parents and that each of the dimensions correspond to the length of each of the parents of C? Basically, I want a program that put those numbers "2", "3" and "4" in the argument of the cell C automatically depending on the length of the parents and C.

An extra example to clarify. Suppose I have extra 2 nodes D and E with 2 and 6 states (D = cell(1,2); and E = cell(1,6);). So, I want that the program creates a new cell C whose dimensions are cretated automatically from its parent nodes, so the program should fill up the argument of the cell C as follows:

C = cell(2,3,2,6,4);

Note that the number of states of the node C has to be at the end of the argument.

Thanks for your help guys!

Best Answer

I'm assuming that your cells will not be individual variables (impossible to work with) but stored for example in another cell array:

function childcell = makecell(parents, numstates)
    %creates a child cell of the correct size based on the size of the parents
    %parents: a cell array of N cell arrays of arbitrary size. 
    %numstates: number of states of the child
    %child cell: the child of size numel(parents{1}) x numel(parents{2}) x ... x numel(parents{N}) x numstates
    validateattributes(parents, {'cell'}, {});
    validateattributes(numstates, {'numeric'}, {'integer', 'scalar', 'positive'})
    parentsizes = cellfun(@numel, parents, 'UniformOutput', false);
    childcell = cell(parentsizes{:}, numstates);
end

Related Solutions

MATLAB: How to construct a cell array from another cell array

This fits the description from your comment under your question. It horizontally concatenates all combinations of the row vectors stored in V{1} and V{2}.

% Demo data
V{1}{1} = 1:4; % vec1 1x4
V{1}{2} = 2:5; % vec2 1x4
V{1}{3} = 3:6; % vec3 1x4
V{2}{1} = 1:3; % vec4 1x3
V{2}{2} = 2:4; % vec5 1x3
[v1idx, v2idx] = ndgrid(1:numel(V{1}), 1:numel(V{2})); 
D = cellfun(@(a,b)horzcat(a,b),{V{1}{v1idx(:)}}, {V{2}{v2idx(:)}}, 'UniformOutput', false)
% D = {[vec1,vec4], [vec2,vec4], [vec3,vec4], [vec1,vec5], [vec2,vec5], [vec3,vec5]}

Version 2: when number of sub-cells in V is variable.

cellCount = num2cell(1:numel(V)); 
nCellIdx = cellfun(@(x)1:numel(x), V, 'UniformOutput', false);
cellGrid = cell(size(nCellIdx)); 
[cellGrid{:}] = ndgrid(nCellIdx{:}); 
matGrid = cell2mat(cellfun(@(x)x(:),cellGrid,'UniformOutput',false)); % Each row is the index for 1 cell
D = cell(1,size(matGrid,1)); 
for i = 1:size(matGrid,1)
    D{i} = cellfun(@(ci,sci)V{ci}(sci),cellCount, num2cell(matGrid(i,:)));
end

D(i) contains the sub-cell indices listed in matGrid(i,:).

MATLAB: How to pick up all combination of numbers from multiple vectors

Don't store your vectors separately. Instead, learn to use tools like cell arrays, which make things hugely more efficient.

V = {[1 2 3],[4 5 6 7],[8 9 10 11 12]};

Next, how do you use a cell array for this purpose? You pass the elements into ndgrid, using what is called acomma separated list. (Or meshgrid.) That is what you get when you type V{:}, a comma separated list. It allows you to pass in each element of the cell array into a function as if each element of the cell array was an argument of the function.

For example, if we did this:

[G1,G2,G3] = ndgrid(V{:});

Hmm. That creates three different arrays, that do contain all combinations of the elements of those vectors if you look carefully. But here we don't want to split the results into n different named arrays. We want a cell array as output. So now, try this:

C = cell(1,numel(V));
[C{:}] = ndgrid(V{:})
C =
  1×3 cell array
    {3×4×5 double}    {3×4×5 double}    {3×4×5 double}

Better. We have captured the output from ndgrid back into a cell array. But what we probably wanted was one flat array, with three columns, and here, 60 rows. We could convert each of those arrays into a column vector easily enough.

C = cellfun(@(X) reshape(X,[],1),C,'UniformOutput',false)
C =
  1×3 cell array
    {60×1 double}    {60×1 double}    {60×1 double}

And, now finally, just convert C into a flat array, using a tool like horzcat. (square brackets will suffice. That is...

C = horzcat(C{:})
C =
     1     4     8
     2     4     8
     3     4     8
     1     5     8
     2     5     8
     3     5     8
     1     6     8
     2     6     8
     3     6     8
     1     7     8
     2     7     8
     3     7     8
     1     4     9
     2     4     9
     3     4     9
     1     5     9
     
     ...
         
     2     7    12
     3     7    12

As you should see, nothing I did was dependent on the size of the arrays, the length of the vectors, the number of different vectors. That was all driven by the one initial cell array as I created it. Learn to use MATLAB, as it was designed to be used.

Best Answer

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MATLAB: How to construct a cell array from another cell array

MATLAB: How to pick up all combination of numbers from multiple vectors

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