Assigning blank cell array confuses Matlab with data type

Question

Dave Lee 2018-12-16

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/435968-assigning-blank-cell-array-confuses-matlab-with-data-type

编辑： Stephen23 2018-12-16

Hi,

I have two cases as below. I want to have both x_cell and x to be single but the first case doesn't give me so. This is the simplified code to represent a bigger problem so it is written in that way because the original code uses parfor so need the blank assigning, and I need to save memory so too many data conversions are not desired. Is there any way to deal with this?

clc;
%% Case 1: assign cell array to be blank
clear all;
x_cell{1} = [];%assigning
for n = 1:10
   x_cell{1}(n) = single(1);%data type we want is single
end
x = x_cell{1};%don't want to make it x=single(x_cell{1}) because the purpose is 
% to make both x_cell and x single to save memory
whos x %this result into double, undesired
%% Case 2: without assigning cell array
clear all;
for n = 1:10
   x_cell{1}(n) = single(1);
end
x = x_cell{1};
whos x %this result into single which is desired

Thanks

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Answer 1

Stephen23 2018-12-16

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/435968-assigning-blank-cell-array-confuses-matlab-with-data-type#answer_352617

编辑：Stephen23 2018-12-16

在 MATLAB Online 中打开

x_cell = {single([])}; % assign.

Note that your code expands the numeric array on each iteration, which is inefficient. It is recommended to preallocate the complete numeric array before the loop, e.g.:

x_cell = {nan(1,10,'single')}; % preallocate.

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html