Strcat multiple cell arrays not outputing expected output

Question

Louis 2016-6-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/289817-strcat-multiple-cell-arrays-not-outputing-expected-output

编辑： Louis 2016-6-14

采纳的回答： Stephen23

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Hello, below is the sample code that I am using to generate cell array of labels

labels = strcat(repmat({'sample'}, 100,1),{'_'}, num2cell([1:100]'));

And I expect to have 100x1 cell with following entries: sample_1; sample_2; sample_3; ... sample_99; sample_100;

However, when I execute the code in MATLAB R2015a, I get the following, which is very confusing...

>> strcat(repmat({'sample'}, 100,1),{'_'}, num2cell([1:100]'))

ans =

    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample'
    'sample_  '
    [1x8 char]
    'sample_'
    'sample_'
    [1x8 char]
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_'
    'sample_ '
    'sample_!'
    'sample_"'
    'sample_#'
    'sample_$'
    'sample_%'
    'sample_&'
    'sample_''
    'sample_('
    'sample_)'
    'sample_*'
    'sample_+'
    'sample_,'
    'sample_-'
    'sample_.'
    'sample_/'
    'sample_0'
    'sample_1'
    'sample_2'
    'sample_3'
    'sample_4'
    'sample_5'
    'sample_6'
    'sample_7'
    'sample_8'
    'sample_9'
    'sample_:'
    'sample_;'
    'sample_<'
    'sample_='
    'sample_>'
    'sample_?'
    'sample_@'
    'sample_A'
    'sample_B'
    'sample_C'
    'sample_D'
    'sample_E'
    'sample_F'
    'sample_G'
    'sample_H'
    'sample_I'
    'sample_J'
    'sample_K'
    'sample_L'
    'sample_M'
    'sample_N'
    'sample_O'
    'sample_P'
    'sample_Q'
    'sample_R'
    'sample_S'
    'sample_T'
    'sample_U'
    'sample_V'
    'sample_W'
    'sample_X'
    'sample_Y'
    'sample_Z'
    'sample_['
    'sample_\'
    'sample_]'
    'sample_^'
    'sample__'
    'sample_`'
    'sample_a'
    'sample_b'
    'sample_c'
    'sample_d'

Could someone help explain this? I appreciate the help in advance!

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Answer 1

Stephen23 2016-6-14

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/289817-strcat-multiple-cell-arrays-not-outputing-expected-output#answer_225469

编辑：Stephen23 2016-6-14

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Explanation

strcat concatenates strings. However num2cell([1:100]') are not strings, they are numeric scalars in a cell array. Where is the string conversion? There isn't any! So strcat thinks that those numeric values are the characters' values, and returns the equivalent character corresponding to each value (some characters are not printable):

 >> char(32:100)
 ans =  !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcd

Solution

To generate strings of those numeric values, try this:

tmp = arrayfun(@num2str,[1:100].','UniformOutput',false)

and also note that you do not need to use repmat or to put the strings 'sample' and '_' into cell arrays: this is a total waste of time and makes the intent of the code much harder to understand. Don't make code more complicated than it needs to be, just do this:

out = strcat('sample_',tmp)

Or you could get rid of the strcat altogether, and just do it using one arrayfun call:

arrayfun(@(n)sprintf('sample_%d',n), [1:100], 'UniformOutput',false)

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Louis 2016-6-14

Thank you!

Louis 2016-6-14

编辑：Louis 2016-6-14

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Thanks for the additional explanation..

Well, the original code looks like this, where the parts of each label rely on the for loop index

for i = 1:n
    for j = 1:m
    labels = [labels; strcat(repmat(strcat(dates(label1{i,2}{j,2}),{'_'},location(i)), 100, 1), {'_'}, arrayfun(@num2str, [1:100].','UniformOutput', false),'.png')];
    end
end