How can I get matlab to execute one or both parts of a code depending on whether a variable exists?

I want to define a cell of data from a particular file if that particular file exists and a different cell of data if a different file exists. Sometimes both files will exist and sometimes only one. I then want to perform some operations on the cell(s) that exist, but a different operation on each existing file. I.e. I might have cell1 and cell2 or I might just have cell1 or just cell2. There will be a set of operations to perform if cell1 exists and a different set of operations to perform if cell2 exists, and if both exist I want to perform both sets of operations. What sort of structure would be best to do this?

Answer 1

[Stephen23]

Avoid checking if variables exist or not (such introspective programming is a path to slow, complex, spaghetti code which is difficult to debug). The clearest code would explicitly indicate if that data has been loaded or not, for which a simple cell array or structure is quite sufficient:

S = struct('data',{[],[]},'loaded',{false,false})
...
S(1).data = ... optionally import file one.
S(1).loaded = true;
...
S(2).data = ... optionally import file two.
S(2).loaded = true;
...
if S(2).loaded % check if file two data has been loaded
    S(2).data % do something ...
end

[S.loaded]  % check if all files have been loaded

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html