How to use accumaray to aggregate text/string based?

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Bayu Ardiyanto 2018-6-8

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https://ww2.mathworks.cn/matlabcentral/answers/404740-how-to-use-accumaray-to-aggregate-text-string-based

评论： Walter Roberson 2018-6-8

Hi!

I know that we can use accumaray for aggregating some value based on key variable, but can we use it to aggregate string as well? My code to aggregate number value:

a=[11;22;22;11;22;11];
b=[10;20;30;10;20;60];
c=['a';'c';'b';'a';'b';'d'];
[i, ~,n]=unique(a,'first'); %find unique
Mode = accumarray(n , b , size(i) , @(x) mode(x)); %find mode based on keys a

This will resulting Mode=[10;20]

For example, I want to use "Mode" for text based variable, i.e. resulting Text=[a,b]

Is it possible to do it? Any help will be appreciated.

Regards!

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Answer 1

Razvan Carbunescu 2018-6-8

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在 MATLAB Online 中打开

accumarray is for numerics only but if c is going to only be single characters then can probably still use accumarray as chars are treated as numerics for most functions.

>> a=[11;22;22;11;22;11]';
>> b=[10;20;30;10;20;60]';
>> c=['a';'c';'b';'a';'b';'d']';
>> [i, ~,n]=unique(a,'first'); %find unique
>> res = accumarray(n , c ,size(i), @mode)
res =
    2×1 char array
      'a'
      'b'

If you want to do grouping for more general text can look at groupsummary or findgroups / splitapply workflow to use with char vectors or strings.

>> t = table(a,b,c);
>> groupsummary(t,'a','mode',{'b' 'c'})
ans =
    2×4 table
      a     GroupCount    mode_b    mode_c
      __    __________    ______    ______
      11        3           10        a   
      22        3           20        b