Elegant way to extract part of a structure as an array
161 visualizaciones (últimos 30 días)
Mostrar comentarios más antiguos
Andrew
el 10 de Mayo de 2011
Comentada: Samuel
el 6 de Dic. de 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 comentarios
Anna Mary Mc Cann
el 18 de Jun. de 2021
If x happened to be a string variable, like a filename, the following works well: char({s(:).x})
Samuel
el 6 de Dic. de 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
Respuesta aceptada
Matt Fig
el 10 de Mayo de 2011
vals = [s(1:2).x]
6 comentarios
Jolanda Müller
el 25 de Sept. de 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
el 11 de Oct. de 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.
Más respuestas (1)
Ver también
Categorías
Más información sobre Matrices and Arrays en Help Center y File Exchange.
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!