CODEWITHSUNDEEP
matlabdata-structuresindexing
Dipole
Dipole

Reputation: 1910

How to do multilevel indexing on array of structs in Matlab?

Let's say I create an array of structs in matlab using:

mystruct = repmat(struct('field1',1, 'field2', ones(10,1)), 10, 1 );

For my purposes (simple example aside), I would find it very useful to get a vector output from using:

myvector = mystruct(:).field2(1)

However this gives me the error:

'Scalar index required for this type of multi-level indexing.'

EDIT: What I expect to get is the first element of the ones vector, from each struct in the array, hence a 10x1 vector of '1'.

I could easily manually using a for loop go through each value in my struct and assign to myvector but that seems incredibly cumbersome and also slow. Any thoughts?

Upvotes: 1

Views: 1987

Answers (2)

sco1
sco1

Reputation: 12214

I'm assuming you're trying to collect all of the field2 vectors into myvector:

myvector = [mystruct(:).field2];

Returns:

myvector =

     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1
     1     1     1     1     1     1     1     1     1     1

EDIT: Per your comment, you can use the above and throw out the data you don't want (myvector(2:end,:) = []; in this case). This is a pretty memory intensive way to do it though. There may be a way to pull what you want using structfun or similar but I'd need to think about how to do it.

EDIT2: Try arrayfun(@(x) x.field2(1), mystruct) and see if this returns what you're looking for.

Upvotes: 1

user1980812
user1980812

Reputation: 81

In two step you can:

  1. get your struct filed2 as a matrix:

    foo = [mystruct.field2];

  2. get the first row (that contains the first indices of the field2)

    myvector = foo(1, :);

Upvotes: 1

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