Create a 1-by-5 categorical vector.

A = categorical({'plane' 'car' 'train' 'car' 'plane'})

A = 1x5 categorical
     plane      car      train      car      plane 

A has three categories. To list the categories and their order, use the categories function. Every element of A belongs to one of the categories listed by the call to categories.

categories(A)

ans = 3x1 cell
    {'car'  }
    {'plane'}
    {'train'}

Find the number of elements in each category of A.

B = countcats(A)

B = 1×3

     2     2     1

The first element in B corresponds to the first category of A, which is car. The second element in B corresponds to the second category of A, which is plane. The third element of B corresponds to the third category of A, which is train.

Since A is a row vector, countcats returns a row vector.

Create a 3-by-2 categorical array, A, from a numeric array.

valueset = 1:3;
catnames = {'red' 'green' 'blue'};

A = categorical([1 3; 2 1; 3 1],valueset,catnames)

A = 3x2 categorical
     red        blue 
     green      red  
     blue       red  

A has three categories, red, green, and blue.

Find the category counts of each column in A.

B = countcats(A)

B = 3×2

     1     2
     1     0
     1     1

The first row of B corresponds to the first category of A. The value, red, occurs once in the first column of A and twice in the second column.

The second row of B corresponds to the second category of A. The value, green, occurs once in the first column of A, and it does not occur in the second column.

The third row of B corresponds to the third category of A. The value, blue, occurs once in the first column of A and once in the second column.

Create a 3-by-2 categorical array, A, from a numeric array.

valueset = 1:3;
catnames = {'red' 'green' 'blue'};

A = categorical([1 3; 2 1; 3 1],valueset,catnames)

A = 3x2 categorical
     red        blue 
     green      red  
     blue       red  

A has three categories, red, green, and blue.

Find the category counts of A along the second dimension.

B = countcats(A,2)

B = 3×3

     1     0     1
     1     1     0
     1     0     1

The first column of B corresponds to the first category of A. The value, red, occurs once in the first row of A, once in the second row, and once in the third row.

The second column of B corresponds to the second category of A. The value, green, occurs in only one element. It occurs in the second row of A.

The third column of B corresponds to the third category of A. The value, blue, occurs once in the first row of A and once in the third row.

Create a 6-by-1 categorical array, A, from a numeric array.

valueset = 1:3;
catnames = {'red' 'green' 'blue'};

A = categorical([1;3;2;1;3;1],valueset,catnames)

A = 6x1 categorical
     red 
     blue 
     green 
     red 
     blue 
     red 

Remove the blue category.

A = removecats(A,'blue')

A = 6x1 categorical
     red 
     <undefined> 
     green 
     red 
     <undefined> 
     red 

A has two categories, red and green. Elements of A that were from the blue category are now undefined.

Find the number of elements in each category of A.

B = countcats(A)

B = 2×1

     3
     1

The first element in B corresponds to the first category of A. The value, red, occurs three times in A.

The second element in B corresponds to the second category of A. The value, green, occurs once in A.

countcats does not return any information on undefined elements.

Use the summary function to view the number of undefined elements in addition to the number of elements in each category of A.

summary(A)

     red              3 
     green            1 
     <undefined>      2