Incorrect use if/else

Question

Alberto Acri 2023-1-11

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1892340-incorrect-use-if-else

评论： Walter Roberson 2023-1-11

Hi. How can I make the following if/else work ?

cell = {[],[],[]};
cell1 = {rand(1452,2),[],[]};
A = cell{1,1};
B = cell1{1,1};
if A = []
    B(:,2)=[];
else
    ....
end

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Answer 1

Star Strider 2023-1-11

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https://ww2.mathworks.cn/matlabcentral/answers/1892340-incorrect-use-if-else#answer_1146595

在 MATLAB Online 中打开

Perhaps this —

cell = {[],[],[]};
cell1 = {rand(1452,2),[],[]};
A = cell{1,1};
B = cell1{1,1};
if isempty(A)
    B(:,2)=[];
else
    % What do you want to do here?
end
B
B = 1452×1
    0.4969
    0.7029
    0.9556
    0.4312
    0.7830
    0.4565
    0.6727
    0.7772
    0.8387
    0.8329

.

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Walter Roberson 2023-1-11

Note that matlab uses == for comparisons.

Exception: if you use a comparison in a symbolic expression, especially a piecewise expression, then the visual representation when you display it might use = instead of == . The visual representation of symbolic expressions is not always valid input to matlab or to the internal symbolic engine either.

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