Why does my cellfun fails?

Question

Javier 2018-10-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423635-why-does-my-cellfun-fails

编辑： Stephen23 2018-10-12

采纳的回答： Stephen23

在 MATLAB Online 中打开

Hello

I have the following cell where I would like to replace all 1 by 'true' and all 0 by 'failed'

 a= [ 0]    [1]    [2]    [3]    [4]    [5]    [6]    [7]    [8]    [9]    [10]    [11]
    [ 1]    [0]    [0]    [0]    [0]    [0]    [0]    [0]    [0]    [0]    [ 0]    [ 0]
    [ 2]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [ 3]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [ 4]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [ 5]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [ 6]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [ 7]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [ 8]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [ 9]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [10]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [0]    [0]    [ 0]    [ 0]
    [11]    [1]    [1]    [1]    [0]    [0]    [1]    [0]    [1]    [0]    [ 0]    [ 0]

If I apply the command

a(cellfun(@(elem) elem == 0,a)) = {'false'}

I get s

 a=   [ false]    [1]    [2]    [3]    [4]    [5]    [6]    [7]    [8]    [9]    [1false]    [11]
      [ 1]    [false]    [false]    [false]    [false]    [false]    [false]    [false]    [false]    [false]    [ false]    [ false]
....

The output expected, however if I try to apply the same command again as

a(cellfun(@(elem) elem == 1,a)) = {'true'}

it fails and matlab says

Error using cellfun
Non-scalar in Uniform output, at index 2, output 1.
Set 'UniformOutput' to false.

Which I don't understand, further if I set the value as indicated I get

a(cellfun(@(elem) elem == 1,a,'UniformOutput',false)) = {'true'}
Function 'subsindex' is not defined for values of class 'cell'.

How can I change the 1 to 'true'?

Thanks in advance

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Kevin Chng 2018-10-12

编辑：Kevin Chng 2018-10-12

sorry, i'm curious how you assign your 'a' variable in MATLAB?

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Answer 1

Stephen23 2018-10-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/423635-why-does-my-cellfun-fails#answer_341062

编辑：Stephen23 2018-10-12

在 MATLAB Online 中打开

"...however if I try to apply the same command again as..."

You have failed to take into account that inbetween running these two commands you have changed the data. So while the first cell array only contained scalar numeric (which is a bad way to store numeric data), the second time you call cellfun the cell array now also contains char vectors (lots of 'false', to be precise). Of course when you compare 'false'==1 then the output will be a vector like this:

>> 'false'==1
ans =
     0     0     0     0     0

and that is clearly not a scalar value, so your cellfun usage will fail unless you use 'uni',false and some more complex processing, or wrap the first argument function in any or something similar. Your third example give this error message

Function 'subsindex' is not defined for values of class 'cell'

because when you use the option 'UniformOutput',false then cellfun outputs a cell array, which cannot be used for indexing. So your attempt to use the output as an index will fail.

Here is a simpler approach using a numeric array (which it should be anyway):

>> m = cell2mat(a);
>> id0 = m==0;
>> id1 = m==1;
>> a(id0) = {'false'};
>> a(id1) = {'true'};
>> a
a = 
    'false'    'true'     [    2]    [    3]    [    4]    [    5]    [    6]    [    7]    [    8]    [    9]    [   10]    [   11]
    'true'     'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'
    [    2]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    3]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    4]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    5]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    6]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    7]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    8]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    9]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [   10]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [   11]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'true'     'false'    'false'    'false'

Note that your row and column headers indicate that you should perhaps be using a table, or only storing the actual data (not the headers) in a simple numeric array. Then you could do this task very simply with some basic indexing:

>> c = {'false','true'};
>> b = c(1+m(2:end,2:end))
b = 
    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'true'     'false'    'false'    'false'