MATLAB: How can i access field values of a struct by indexing

arrayfieldindexingMATLABmatrixstructures

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

Best Answer

a = structfun(@(F) F(1:100,:), b, 'uniform', 0)

Related Solutions

MATLAB: ‘Subscripted assignment between dissimilar structures’ thrown on empty struct

Like any MATLAB array, it is bad to iteratively concatenate to a struct array because it forces lots of unnecessary memory reallocation. It would be better if you pre-allocate the array by doing

 N=length(input);
 struct_array(N)=struct('field1",[],'field2',[]);
 for i=1:N
  struct_array(i)=struct_fn(input(i));
 end

Alternatively, instead of pre-allocating before the loop, you could also loop backwards so that all memory allocation is done in the first iteration of the loop.

 for i=N:-1:1
  struct_array(i)=struct_fn(input(i));
 end

MATLAB: Whats a fast method for keeping only a subset of fields from a structure

Matlab's RMFIELD contains some inefficient time-wasters. Use the faster C-Mex function:

http://www.mathworks.com/matlabcentral/fileexchange/28517-frmfield

The actual values are created as shared data copied, such that the memory is used efficiently. The submission contains an M-Version also, which works equivalent to:

F = fieldnames(S);
D = struct2cell(S);
keep = ~mask;  % As in your example
S = cell2struct(D(keep), F(keep));

But in a real implementation you have to consider struct arrays, removing all existing fields and other exceptions. Therefore I'd prefer the Mex.

Best Answer

Related Solutions

MATLAB: ‘Subscripted assignment between dissimilar structures’ thrown on empty struct

MATLAB: Whats a fast method for keeping only a subset of fields from a structure

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