When is it appropriate to use a cell array vs. a struct in Matlab?

Question

If I want to store some strings or matrices of different sizes in a single variable, I can think of two options: I could make a struct array and have one of the fields hold the data,

structArray(structIndex).structField

or I could use a cell array,

cellArray{cellIndex}

but is there a general rule-of-thumb of when to use which data structure? I'd like to know if there are downsides to using one or the other in certain situations.

Answer 1

In my opinion it's more a matter of convenience and code clarity. Ask yourself would you prefer to refer your variable elements by number(s) or by name. Then use cell array in former case and struct array in later. Think about it as if you have a table with and without headers.

By the way you can easily convert between structures and cells with CELL2STRUCT and STRUCT2CELL functions.

Answer 2

If you use it for computation within a function, I suggest you use cell arrays, since they're more convenient to handle, thanks e.g. to CELLFUN.

However, if you use it to store data (and return output), it's better to return structures, since the field names are (should be) self-documenting, so you don't need to remember what information you had in column 7 of your cell array. Also, you can easily include a field 'help' in your structure where you can put some additional explanation of the fields, if necessary.

Structures are also useful for data storage since you can, if you want to update your code at a later date, replace them with objects without needing to change your code (at least in case you did pre-assignment of your structure). They have the same sytax, but objects will allow you to add more functionality, such as dependent properties (i.e. properties that are calculated on the fly based on other properties).

Finally, note that cells and structures add a few bytes of overhead to every field. Thus, if you want to use them to handle large amounts of data, you're much better off to use structures/cells containing arrays, rather than having large arrays of structures/cells where the fields/elements only contain scalars.