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How can i access field values of a struct by indexing?

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Henning Wilhelm
Henning Wilhelm 2017-11-6
评论： Walter Roberson 2021-1-26
My struct has several fields containing a matrix. How can I get the first 100 values of each field without using a for loop.
a = b.(fieldnames(b))(1:100,:); % wont work

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Walter Roberson
Walter Roberson 2017-11-6
a = structfun(@(F) F(1:100,:), b, 'uniform', 0)
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Rik
Rik 2021-1-26
That is true in general. The best you can hope for is parity (given proper pre-allocation). Every function that hides a loop (cellfun, arrayfun, etc) will have an overhead. Matlab is getting better and better at for-loops.
The only exception to this rule is if you have actual array operations:
%slow:
s=0;for n=1:numel(data),s=s+data(n);end
%fast
s=sum(data);
Walter Roberson
Walter Roberson 2021-1-26
Anonymous functions are more expensive than plain function handles such as @sin

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