Onehotencode function is giving more columns which are filled with zeros than the number of categories.

a = readtable("mushrooms.csv");

aa = categorical(table2array(a));

b = onehotencode(aa(:,1),2);

first column has 2 categories but function creates 23 columns. Which is also the total number of columns in variable a. Also other variables behave the same too and seemingly 2 spesific column in each onehotencoded variable has the true onehotencoded variables. Can you help me please?

Answer 1

[Mohammad Sami]

Because you are converting the entire matrix in to a categorical matrix, the categories for the entire matrix are common. If you want to have different categories for each column. you will have to convert each columm to caterogical separately.

a = repmat(1:10,10,1);
b = categorical(a)

b = 10×10 categorical array
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 
     1      2      3      4      5      6      7      8      9      10 

categories(b(:,1))

ans = 10×1 cell array
    {'1' }
    {'2' }
    {'3' }
    {'4' }
    {'5' }
    {'6' }
    {'7' }
    {'8' }
    {'9' }
    {'10'}

c = array2table(a);
c = varfun(@categorical,c)

c = 10×10 table
    categorical_a1    categorical_a2    categorical_a3    categorical_a4    categorical_a5    categorical_a6    categorical_a7    categorical_a8    categorical_a9    categorical_a10
    ______________    ______________    ______________    ______________    ______________    ______________    ______________    ______________    ______________    _______________

          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       
          1                 2                 3                 4                 5                 6                 7                 8                 9                 10       

categories(c{:,1})

ans = 1×1 cell array
    {'1'}

Answer 2

[Yagiz Dereboy]

Thanks!!