Preallocating a cell array of chars?

Question

Monika Jaskolka 2020-10-27

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/627858-preallocating-a-cell-array-of-chars

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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Answer 1

Stephen23 2020-10-27

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https://ww2.mathworks.cn/matlabcentral/answers/627858-preallocating-a-cell-array-of-chars#answer_525848

编辑：Stephen23 2020-10-27

在 MATLAB Online 中打开

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);

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Monika Jaskolka 2020-10-27

在 MATLAB Online 中打开

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.