Elegant way to extract part of a structure as an array

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Andrew
Andrew 2011-5-10
评论： Samuel 2023-12-6
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
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Anna Mary Mc Cann
Anna Mary Mc Cann 2021-6-18
If x happened to be a string variable, like a filename, the following works well: char({s(:).x})
Samuel
Samuel 2023-12-6
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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采纳的回答

Matt Fig
Matt Fig 2011-5-10
vals = [s(1:2).x]
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Jolanda Müller
Jolanda Müller 2023-9-25
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 2023-10-11
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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更多回答（1 个）

Marko Usaj
Marko Usaj 2017-11-10
Amazing! Thank you very much!

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