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Creating an array of structs and using the field directly?

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Jan Kappen
Jan Kappen on 19 Nov 2015
Commented: Jan on 23 Nov 2015
Hey guys. I'm wondering if there is a workaround for doing something like this:
a = {[struct('field',1) struct('field',2)].field}
which works in octave but not in matlab ("invalid syntax at '.'. Possibly a ')', ']' or '}' is missing"), I have to use a temporary variable. This is quite annoying. Is there a workaround?
Thanks!

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Accepted Answer

Stephen Cobeldick
Stephen Cobeldick on 19 Nov 2015
Edited: Stephen Cobeldick on 19 Nov 2015
It is not clear why you need to structure at all, as the output is simply a cell array with some numeric scalars in it (Octave code below)
>> {[struct('field',1) struct('field',2)].field}
ans =
{
[1,1] = 1
[1,2] = 2
}
>> {struct('field',{1,2}).field}
ans =
{
[1,1] = 1
[1,2] = 2
}
>> {1,2}
ans =
{
[1,1] = 1
[1,2] = 2
}
If the input is already a structure, then you can simply access the field values using the methods given in the documentation for non-scalar structures:
{X.field}

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Stephen Cobeldick
Stephen Cobeldick on 20 Nov 2015
Good question, but as you have only given us one line of code it is impossible for us to know what the entire code is doing. All we know is that your code concatenates two scalar structures together, so most likely there are more efficient ways of handling this. Without any explanation of what the code does and its requirements there is not much point to giving any more detailed advice.
Jan Kappen
Jan Kappen on 20 Nov 2015
Sorry, you're right of course. But you explicitely mentioned the "proper usage of non-scalar arrays", so I thought there is a obvious mistake?
Stephen Cobeldick
Stephen Cobeldick on 20 Nov 2015
Again it depends on what you mean by "mistake": perhaps you need to have two scalar structures, this I do not know. See my answer for one way of defining a non-scalar structure using a single call to struct.

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More Answers (1)

Jan
Jan on 19 Nov 2015
As long as you insist on using standard struct : No, there is no workaround. Using a temporary variable is not a big deal and does not waste additional resources.
You can create your own object class, which solves the problem. But this will be less efficient.

  3 Comments

Jan Kappen
Jan Kappen on 19 Nov 2015
Okay thank you. Of course using a temporary variable isn't that big deal, it's just for clear- and mayby laziness ;)
Jan Kappen
Jan Kappen on 20 Nov 2015
Can I accept both answers as correct answers, since they both are correct?
Jan
Jan on 23 Nov 2015
You can accept one answer only. But you can vote for more answers and a comment is useful also.

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