Data and variable management

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Tolulope
Tolulope on 8 May 2013
I would like to know how to pass lots of variables efficiently between functions.
At the moment, I have close to 30 m.files. All file are either functions or scripts. I have tried to organised my code as best as I can in groups of functions the perform as single task. Once a stage of analysis is completed, the code/evaluation moves to the next group of functions. For example,
1. Stage 1 group of functions, sub-functions and scripts: Loads data 2. Stage 2 group of funcs, subfuncs and scripts: Analyses loaded data 3. Stage 3 group of funcs, subfuncs and scripts: Generates some basic plots
I notice that passing so many variables between functions is getting tricky. For example, let's say there's a variable evaluated in Stage 1 that's useful in Stage 3. Now let's say it's evaluated in a third tier sub-function (a sub-function of a sub-function of a function), I would assign the variable out (often with "varargout"), all the way to top tier function, and then pass it all the way down to desired function in Stage 3.
My knowledge of MatLab is pretty basic, my knowledge of programming even less. So I have avoided using things like structures and callbacks. I only use scripts, functions and arrays.
Is there a better way of passing variables around between functions?

Accepted Answer

the cyclist
the cyclist on 8 May 2013
You mention "avoiding" structures, but I would say this is definitely one solution. They are not that difficult to learn. Here is one starting point: http://www.mathworks.com/help/matlab/structures.html
Another possibility, which may or may not be feasible (depending on the size of the variables), would be to write/read the variables to disk, using the save() and load() commands. Maybe not the best programming practice, but easy.
Speaking of questionable programming practices, you could also use global variables. This may be appropriate if the same variable are really shared by a lot of function.
>> doc global
for details.
  1 Comment
Tolulope
Tolulope on 8 May 2013
Thanks
Yes, I too had come across warnings against using global variables and binary file systems, that was what perhaps dissuaded me using from them. But since the project does not require much user input, it may be worth looking into.

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More Answers (2)

David Sanchez
David Sanchez on 8 May 2013
You should start thinking on either global or struct variables....or a global struct. For example: define a global variable by typing
global my_global_var %(any name to your liking is valid)
right after the function definition.
function my_fun
global my_global_var
% function code here
Then, add my_global_var. as a prefix to all your variables: if you had a variable called xxx, rename it my_global_var.xxx
Your functions/scripts can use the variables and change them. Changes will be applied globally.

Jason Ross
Jason Ross on 8 May 2013
I would recommend using structures versus using globals. Global variables have the potential to cause problems which are extremely difficult to diagnose which can lead directly to bizarre behavior by your code when you have to track where something is being changed.
Don't just take my word for -- the collected wisdom that is Wikipedia gets right into why global variables are a bad idea (in any language!) in the second paragraph:
  2 Comments
Jason Ross
Jason Ross on 8 May 2013
If you are worried about space, you can check the size with the whos function.
You also don't have to do everything in one giant struct, you can pass elements in where appropriate (e.g. myFunction(mystruct.myfield)) if you don't want to ship everything in. You could also use multiple structs, too, if that might make sense.

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