Question

I am writing a function to remove some values from a cell array, like so:

function left = remove(cells, item);
left = cells{cellfun(@(i) ~isequal(item, i), cells)};

But when I run this, left has only the first value, as the call to cells{} with a logical array returns all of the matching cells as separate values. How do I group these separate return values into a single cell array?

Also, perhaps there is already a way to remove a given item from a cell array? I could not find it in the documentation.

Answer 1

You have to use () instead of {} to index the cells:

function left = remove(cells, item)
  left = cells(cellfun(@(i) ~isequal(item, i), cells));

Using () for indexing will give you a subset of cells, while using {} will return the contents of a subset of cells as a comma-separated list, and only the first entry of that list will get placed in left in your example.

You can check out this MATLAB documentation for more information on using cell arrays.

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EDIT: Response to comment…

If you have an operation that ends up giving you a comma-separated list, you can place the individual elements of the list into cells of a cell array by surrounding the operation with curly braces. For your example, you could do:

left = {cells{cellfun(@(i) ~isequal(item, i), cells)}};

The inner set of curly braces creates a comma-separated list of the contents of cells that are not equal to item, and the outer set then collects this list into a cell array. This will, of course, give the same result as just using parentheses for the indexing, which is the more sensible approach in this case.

If you have a function that returns multiple output arguments, and you want to collect these multiple values into a cell array, then it’s a bit more complicated. You first have to decide how many output arguments you will get, or you can use the function NARGOUT to get all possible outputs:

nOut = 3;                   %# Get the first three output arguments
%# Or...
nOut = nargout(@some_fcn);  %# Get all the output arguments from some_fcn

Then you can collect the outputs into a 1-by-nOut cell array outArgs by doing the following:

[outArgs{1:nOut}] = some_fcn(...);

It should be noted that NARGOUT will return a negative value if the function has a variable number of output arguments, so you will have to choose the value for nOut yourself in such a case.