Nesting depth and the error "Expected one output from a curly brace or dot indexing expression, but there were x results."

조회 수: 4 (최근 30일)
Consider this toy example:
a(1).x.y=1
a(2).x.y=2
[a.x.y]
Why does this produce the infamous error
Expected one output from a curly brace or dot indexing expression, but there were 2 results.
..instead of just listing all values from across all indexed structure elements, as in this other example where the nesting is at level 2 instead of level 3:
a(1).x=1
a(2).x=2
[a.x]
>> [a.x]
ans =
1 2

채택된 답변

Bruno Luong
Bruno Luong 2022년 8월 19일
편집: Bruno Luong 2022년 8월 19일
a work around if you insist on oneline
a(1).x.y=1
a = struct with fields:
x: [1×1 struct]
a(2).x.y=2
a = 1×2 struct array with fields:
x
axy = [struct([a.x]).y]
axy = 1×2
1 2

추가 답변 (1개)

Jan
Jan 2022년 8월 19일
R2022a creates a different error:
a(1).x.y=1;
a(2).x.y=2;
[a.x.y]
Intermediate dot '.' indexing produced a comma-separated list with 2 values, but it must produce a single value when followed by subsequent indexing operations.
"instead of just listing all values from across all indexed structure elements"
Think twice. [a.x] is an array already with 2 elements. The dot operator cannot handle an array as input, but a scalar struct only. This is plausible. Consider, that there is no logical decision for the dimensions of the output. It is also unclear, what you call "just listing all values".
  댓글 수: 3
Image Analyst
Image Analyst 2022년 8월 19일
Is there a bracket/brace/parentheses solution to this, or is the only way a simple but intuitive for loop
a(1).x.y=1;
a(2).x.y=2;
all_y = zeros(numel(a), 1);
for k = 1 : numel(a)
all_y(k) = a(k).x.y;
end
or possibly a cryptic call to structfun or some other weird function
Stephen23
Stephen23 2022년 8월 19일
"The dot operator cannot handle an array as input, but a scalar struct only."
???
a(1).x.y=1;
a(2).x.y=2;
tmp = [a.x] % array struct, not scalar struct
tmp = 1×2 struct array with fields:
y
[tmp.y] % dot indexing accepts an array without any problem
ans = 1×2
1 2

댓글을 달려면 로그인하십시오.

카테고리

Help CenterFile Exchange에서 Migrate GUIDE Apps에 대해 자세히 알아보기

제품


릴리스

R2019b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by