How to access multiple fields in a struct by a vector of indices?

Hi Everyone,

I have a struct

a

with fields that is of the form:

f1: [5×5 double]
f2: [5×5 double]
f3: [5×5 double]
f4: [5×5 double]
f5: [5×5 double]

I also have a vector of indices

idx = [2,3,4]

and would like to access/extract the fields in a indexed by idx (i.e., f2,f3,f4). Is there a clever and convenient way to accomplish this without using, for instance, fieldnames in combination with a for loop?

Thanks and all best,

M.

[Stephen23]

"Is there a clever and convenient way to accomplish this without using, for instance, fieldnames in combination with a for loop?"

Not really, because fields are not designed to represent a particular sequence - their order can be changed, without changing their names. A sequence is best represented by an index: its order is fixed, simply by definition of the index itself. This means the two are not equivalent, and there is no general solution to convert between fieldnames and indices.

If you want to access something with indices, then why are you using fieldnames? Probably you should instead be using a non-scalar structure with efficient indexing, and avoid using slow numbered fieldnames altogether.

[Mario Goldenbaum]

Stephen, thanks much for your comment. I agree with you. The simple answer is that I got tons of data stored this way. And now I have to deal with it.

Answer 1

[Adam Danz]

There isn't a set method but here are some options.

Option 1 : Convert to cell array

sCell = struct2cell(s)
sCell(idx)

Option 2: Use a non-scalar structure instead

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

[Mario Goldenbaum]

Hi Adam,

Thanks much for this. It works.

Best, M.