How do I name this variable dynamically?

I am trying to fetch a series of simulation runs from a computer, and the following works just fine:

dataset = j1.fetchOutputs{:};

However, I have more than simply j1. I have j1 to ji. So, I thought looping through 1:i using the following line would work, but it doesn't:

batch = sprintf('j%d' ,i)

and then

dataset = batch.fetchOutputs{:};

I get the error:

"Struct contents reference from a non-struct array object". Can someone help me out here?

Answer 1

[Stephen23]

http://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 2

[Henry Giddens]

In your example above, the variable "batch" is a string. You cant reference object properties or methods, or structure fields from a string, which is what the error message is telling you.

In answer to your question for dynamically addressing variable names, you can use 'eval'

batch = eval(sprintf('j%d' ,i));
dataset = batch.fetchOutputs
% or
% dataset = eval(sprintf('j%d.fetchOutputs{:});

A better way i guess would be to store all the variables "j1" to "ji" as inputs to an array when they are created, rather than as seperate variables. Then you would just need to reference each entry in the array and avoid using eval.

[Stephen23]

Let me quote Steve Lord, who works for TMW (the company that make MATLAB):

" DO NOT USE EVAL."

I know, beginners always think that magically making variables pop into existence is a great idea. It isn't. It is slow and buggy, and those beginners should take the time to learn from Steve Lord and other MATLAB experts who show much faster and more efficient ways to write code.

[Henry Giddens]

Just to say that I agree, and don't ever use it myself (Don't really know why I suggested it...). Thanks Stephen for giving a good explanation as to why its a bad idea!