arrays - 如何在 Matlab 中将结构体的叶子作为向量返回？

Question

我经常需要访问结构化数组中的数据叶子进行计算。 在 Matlab 2017b 中如何最好地完成此操作？

% Minimal working example:
egg(1).weight = 30;
egg(2).weight = 33;
egg(3).weight = 34;

someeggs = mean([egg.weight]) % works fine

apple(1).properties.weight = 300;
apple(2).properties.weight = 330;
apple(3).properties.weight = 340;

someapples = mean([apple.properties.weight]) %fails
weights = [apple.properties.weight] %fails too

% Expected one output from a curly brace or dot indexing expression, 
% but there were 3 results.

Answer 1

如果只有顶层是非标量 structure array ，并且下面的每个条目都是标量结构，您可以通过调用 arrayfun 来收集叶子。 ，然后对返回的向量进行计算:

>> weights = arrayfun(@(s) s.properties.weight, apple)  % To get the vector

weights =

   300   330   340

>> someapples = mean(arrayfun(@(s) s.properties.weight, apple))

someapples =

  323.3333

[apple.properties.weight] 失败的原因是点索引返回 comma-separated list apple.properties 的结构。您需要将此列表收集到一个新的结构数组中，然后对下一个字段weight应用点索引。