Elegant way to extract part of a structure as an array

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Andrew
Andrew am 10 Mai 2011
Kommentiert: Samuel am 6 Dez. 2023
Hi,
I would like to be able to extract part of a structure as an array. For example, suppose I create a simple structure:
s(1).x=1;
s(1).y=2;
s(2).x=3;
s(2).y=4;
s(3).x=5;
s(3).y=6;
Now suppose I want to extract the x values for the first two parts of this structure (that is, (1).x and (2).x). So I try:
>> s([1 2]).x
ans =
1
ans =
3
I get the x values for (1) and (2), but as two separate outputs. So if I make an assignment like the following:
>> vals=s([1 2]).x
vals =
1
It only captures the first of the two outputs. I can get around this by putting the result of s([1 2]).x in a cell array, using curly braces:
>> vals={s([1 2]).x}
vals =
[1] [3]
But I actually don't want these values in a cell array; I would like them an array, with each value in a row. I can do this by the following:
>> vals=cell2mat({s([1 2]).x}')
vals =
1
3
Now I have what I want. But, my question is, is there an easier, more elegant way to do this? My conversion of the output from array to cell array and then back to array seems very convoluted.
Thanks in advance.
Andrew DeYoung
Carnegie Mellon University
  7 Kommentare
Anna Mary Mc Cann
Anna Mary Mc Cann am 18 Jun. 2021
If x happened to be a string variable, like a filename, the following works well: char({s(:).x})
Samuel
Samuel am 6 Dez. 2023
An easier way to do this would be simply typing:
vals = [s([1 2]).x]
or
vals = [s([1 2]).x]'
to get a row/column vector for the answers to s(1).x and s(2).x

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Akzeptierte Antwort

Matt Fig
Matt Fig am 10 Mai 2011
vals = [s(1:2).x]
  6 Kommentare
Jolanda Müller
Jolanda Müller am 25 Sep. 2023
This is great, but what would be an equivalent of this if I have a more nested struct?
e.g.
s(1).x.a = 1
s(1).x.b = 10
s(1).y = 'one'
s(2).x.a = 2
s(2).x.b = 20
s(2).y = 'two'
When trying to get the array
[s.x.a]
it throws an error saying "Intermediate dot '.' indexing produced a comma-separated list with 2 values, but it must produce a single value when followed by subsequent indexing operations."
Is there an elegant way to do an equivalent to [s.x.a] that does not throw an error? The output I would like to see in this example would be [1 2].
Derek Sherry
Derek Sherry am 11 Okt. 2023
It's not quite as pretty, but it does seem you can do it if you use two lines rather than one.
x = [s.x]
This bit creates a struct with just the information associated with x.
Then
[x.a]
should give you the output [1 2] that you're looking for.

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Weitere Antworten (1)

Marko Usaj
Marko Usaj am 10 Nov. 2017
Amazing! Thank you very much!

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