在不循环访问matlab中访问多个结构字段

Question

我有一个 8x18 结构，每个单元格包含单个事件发生的列向量。我想从这些连接在单个数组中的一些字段中获取数据，而不必遍历它。我似乎找不到将我感兴趣的字段垂直连接到一个数组中的方法。

作为示例，我创建了以下结构，每个单元格出现 1 到 5 次：

s(62).vector(8,18).heading.occurrences=[1;2;3];
for i=1:62
    for j=1:8
        for k=1:18
            y=ceil(rand(1)*5);
            s(i).vector(j,k).heading.occurrences=rand(y,1);
        end
    end
end

现在，如果想要获得多个单元格中的所有出现，同时保持 i 恒定不变 i=1，则以下工作：

ss=s(1).vector([1 26 45]);                     
h=[ss.heading];            
cell2mat({h.occurrences}')

现在我想为 s 做同样的事情，例如 s([1 2 3]).vector([1 26 45])，那将如何工作？我试过 xx=s([1 2 3])、yy=xx.vector([1 26 45]) 但这会产生错误：

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

矢量运算也可以做到这一点吗？

Answer 1

很难向量化整个操作，但这应该可行。

% get vector field and store in cell array
s_new = { s(1:3).vector };

% now extract heading field, this is a cell-of-cells
s_new_heading = cellfun(@(x) { x.heading }', s_new, 'UniformOutput', false);

occurences = {};
for iCell = 1:length(s_new_heading)
    % use current cell
    cellHere = s_new_heading{iCell};

    % retain indices of interest, these could be different for each cell
    cellHere = cellHere([ 1 26 45 ]);

    % extract occurrences
    h = cellfun(@(x) x.occurrences, cellHere, 'UniformOutput', false);
    h_mat = cell2mat(h);

    % save them in cell array 
    occurences = cat(1, occurences, h_mat);
end

Answer 2

这是一个向量化的解决方案，可以为 s 和字段 vector:

使用索引向量

sIndex = [1 2 3];    % Indices for s
vIndex = [1 26 45];  % Indices for 'vector' field

v = reshape(cat(3, s(sIndex).vector), 144, []);
h = [v(vIndex, :).heading];
out = vertcat(h.occurrences);

它使用cat to concatenate all the vector fields into an 8-by-18-by-numel(sIndex) matrix, reshapes that into a 144-by-numel(sIndex) matrix, then indexes the rows specified by vIndex and collects their heading and occurrences fields, using vertcat instead of cell2mat。

在不循环访问matlab中访问多个结构字段

Acessing multiple structure fields in matlab without looping through it

matlab

matlab-struct