Extracting variables from a struct array with many empty structs

Question

Sam Da 2012-10-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/51634-extracting-variables-from-a-struct-array-with-many-empty-structs

I have a giant struct array and many of which are empty.

struct array with fields: f1, f2, f3. i.e. Struct Array: StAr(i,j) has StAr(i,j).f1, StAr(i,j).f2,StAr(i,j).f3. But I want to create a new Array by just collecting all the f1 values without using a for loop.

(1) Since many of the structs in the array are empty when I do [StrAr.f1] it gives me a row vector from the non-empty structs. How do I substitute the empty struct values with 0 instead of a matrix.

or

(2) Just get the index of non-empty structs?

Thanks guys

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Answer 1

Andrei Bobrov 2012-10-23

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https://ww2.mathworks.cn/matlabcentral/answers/51634-extracting-variables-from-a-struct-array-with-many-empty-structs#answer_62923

编辑：Andrei Bobrov 2012-10-24

在 MATLAB Online 中打开

k = {StAr.f1};
out = zeros(size(k));
nonempty = ~cellfun(@isempty,k);
out(nonempty) = [StAr.f1]; % (1)
idx = find(nonempty);      % (2)

EDIT

k = {StAr.f1};
k1 = cellfun(@(x)x(:).',k,'un',0);
ii = cellfun(@isempty,k1);
k1(ii) = {0};
out = cell2mat(k1); % (1)
idx = find(ii);    % (2)

EDIT 2

k = reshape({StAr.f1},size(StAr));
k2 = cellfun(@(x)x(:).',k,'un',0);
ii = cellfun(@isempty,k2);
k2(ii) = {nan};
s2 = cellfun('size',k2,2);
out = cell2mat(cellfun(@(x,y)[x,nan(1,y - numel(x))],...
                               k2,num2cell(ones(size(s2,1),1)*max(s2)),'un',0));

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Sam Da 2012-10-23

In this step: k = {StAr.f1};

the original array structure is flattened out to be a row vector. Can I preserve the array structure and keep it m x n. I am not great with Matlab so please excuse my silly questions.