Preallocating a cell array of chars?

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Monika Jaskolka
Monika Jaskolka 2020-10-27
评论： Monika Jaskolka 2020-10-27
Is there a better way of preallocating a cell array of empty chars than using a for loop or deal? Cells can contain any data type, yet if I create a empty cell array, it is always type double.
>> A = cell([3,1])
A =
3×1 cell array
{0×0 double}
{0×0 double}
{0×0 double}
>> for i = 1:length(A), A{i} = ''; end
>> A
A =
3×1 cell array
{0×0 char}
{0×0 char}
{0×0 char}

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采纳的回答

Stephen23
Stephen23 2020-10-27
编辑：Stephen23 2020-10-27
A = cell(3,1);
A(:) = {''}
This assigns one scalar cell (on the RHS) to all of the cells in the array A:
https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html
Or simply use
A = repmat({''},3,1);
  1 个评论
Monika Jaskolka
Monika Jaskolka 2020-10-27
Thanks. Looks like the your first approach is fastest for my case.
>> len = 1000000;
>> A = cell([len, 1]); tic; A(:) = {''}; toc % assignment
Elapsed time is 0.013068 seconds.
>> A = cell([len, 1]); tic; A = repmat({''},len,1); toc % repmat
Elapsed time is 0.024813 seconds.
>> A = cell([len, 1]); tic; for i = 1:length(A), A{i} = ''; end, toc % for loop
Elapsed time is 0.183295 seconds.
>> A = cell([len, 1]); tic; [A{:}] = deal(''); toc % deal
Elapsed time is 0.293894 seconds.

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