How to create an empty dictionary with a struct as value

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Guido Hiller
Guido Hiller 2022-12-8
评论： Guido Hiller 2022-12-9
Ran in:
I want to create a dictionary with a defined struct as the value. What i currently have is:
dict = dictionary(string.empty, struct(test={}));
The problem is that the empty dictionary throws an error when i try to access the struct it throws an error that the field name does not exist:
dict.values.test
Unrecognized field name "test".
I want that the dictionary behave like when you try to access an empty struct with a field. Is there any way so the dictionary remembers the field values?
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Paul
Paul 2022-12-9
Ran in:
@Guido Hiller
I still don't understand what the use case is for having an empty, configured dictionary where the value of the empty dictionary is a struct with a field. What would you do with that empty dictionary, which I guess is the same question asked by @Jan.
If we configure a dictionary with an empty string key and empty struct value
d = dictionary(string.empty,struct.empty)
d =
dictionary (string ⟼ struct) with no entries.
we can subsequently add entries to the dictionary
d("a") = struct(test=1);
d("b") = struct(test=2);
d.values returns a struct array
d.values
ans = 2×1 struct array with fields:
test
which, in this case can be accessed as a struct and the values in the test field turned into an array via a comma separated list in the usual way
[d.values.test]
ans = 1×2
1 2
We can add an entry with a different type of value in the test field
d("c") = struct(test="foo")
d =
dictionary (string ⟼ struct) with 3 entries: "a" ⟼ 1×1 struct "b" ⟼ 1×1 struct "c" ⟼ 1×1 struct
d.values
ans = 3×1 struct array with fields:
test
d.values.test
ans = 1
ans = 2
ans = "foo"
We can even add a struct with a different field
d("d") = struct(other=100)
d =
dictionary (string ⟼ struct) with 4 entries: "a" ⟼ 1×1 struct "b" ⟼ 1×1 struct "c" ⟼ 1×1 struct "d" ⟼ 1×1 struct
But now we can't access values as above because the struct values are different and can't themeselves be concateneated into a struct array
try
d.values
catch ME
disp('error')
end
error
But we can still get the values in a cell array
values(d,"cell")
ans = 4×1 cell array
{1×1 struct} {1×1 struct} {1×1 struct} {1×1 struct}
Guido Hiller
Guido Hiller 2022-12-9
@Paul Thank you for your answer. I think I had a misunderstanding about the behaviour of structs. If you can put structs with different fields into the same dictionary, then my inital question does not make any sense.

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