Combine Categorical Arrays

This example shows how to combine categorical arrays.

Create Categorical Arrays

Create a categorical array that contains the preferred lunchtime beverage of 25 students in classroom A.

rng("default")
A = randi(3,[25,1]);
A = categorical(A,1:3,["milk" "water" "juice"])

A = 25x1 categorical
     juice 
     juice 
     milk 
     juice 
     water 
     milk 
     milk 
     water 
     juice 
     juice 
     milk 
     juice 
     juice 
     water 
     juice 
     milk 
     water 
     juice 
     juice 
     juice 
     water 
     milk 
     juice 
     juice 
     juice 

Summarize the categorical array.

summary(A)

A: 25x1 categorical

     milk              6 
     water             5 
     juice            14 
     <undefined>       0 

Create another categorical array that contains the preferences of 28 students in classroom B.

B = randi(3,[28,1]);
B = categorical(B,1:3,["milk" "water" "juice"])

B = 28x1 categorical
     juice 
     juice 
     water 
     water 
     milk 
     juice 
     milk 
     milk 
     milk 
     milk 
     juice 
     juice 
     milk 
     juice 
     milk 
     water 
     water 
     juice 
     juice 
     milk 
     water 
     water 
     water 
     juice 
     juice 
     milk 
     juice 
     water 

Summarize the categorical array.

summary(B)

B: 28x1 categorical

     milk              9 
     water             8 
     juice            11 
     <undefined>       0 

Concatenate Categorical Arrays

Concatenate the data from classrooms A and B into a single categorical array, Group1.

Group1 = [A;B]

Group1 = 53x1 categorical
     juice 
     juice 
     milk 
     juice 
     water 
     milk 
     milk 
     water 
     juice 
     juice 
     milk 
     juice 
     juice 
     water 
     juice 
     milk 
     water 
     juice 
     juice 
     juice 
     water 
     milk 
     juice 
     juice 
     juice 
     juice 
     juice 
     water 
     water 
     milk 
      ⋮

Summarize the categorical array, Group1.

summary(Group1)

Group1: 53x1 categorical

     milk             15 
     water            13 
     juice            25 
     <undefined>       0 

Create Categorical Array with Different Categories

Create a categorical array, Group2, that contains data from 50 students who were given the additional beverage option of soda.

Group2 = randi(4,[50,1]);
Group2 = categorical(Group2,1:4,["juice" "milk" "soda" "water"])

Group2 = 50x1 categorical
     juice 
     juice 
     milk 
     water 
     milk 
     soda 
     juice 
     water 
     milk 
     soda 
     soda 
     water 
     water 
     soda 
     juice 
     juice 
     milk 
     water 
     milk 
     water 
     juice 
     water 
     milk 
     juice 
     milk 
     soda 
     milk 
     milk 
     water 
     soda 
      ⋮

Summarize the categorical array.

summary(Group2)

Group2: 50x1 categorical

     juice            12 
     milk             14 
     soda             10 
     water            14 
     <undefined>       0 

Concatenate Arrays with Different Categories

Concatenate the data from Group1 and Group2.

students = [Group1;Group2]

students = 103x1 categorical
     juice 
     juice 
     milk 
     juice 
     water 
     milk 
     milk 
     water 
     juice 
     juice 
     milk 
     juice 
     juice 
     water 
     juice 
     milk 
     water 
     juice 
     juice 
     juice 
     water 
     milk 
     juice 
     juice 
     juice 
     juice 
     juice 
     water 
     water 
     milk 
      ⋮

Summarize the resulting categorical array. Concatenation appends the categories exclusive to the second input, soda, to the end of the list of categories from the first input, milk, water, juice, soda.

summary(students)

students: 103x1 categorical

     milk             29 
     water            27 
     juice            37 
     soda             10 
     <undefined>       0 

To change the order of the categories in the categorical array, use the reordercats function.

students = reordercats(students,["juice" "milk" "water" "soda"]);

categories(students)

ans = 4x1 cell
    {'juice'}
    {'milk' }
    {'water'}
    {'soda' }

Union of Categorical Arrays

To find the unique responses from Group1 and Group2, use the union function.

C = union(Group1,Group2)

C = 4x1 categorical
     milk 
     water 
     juice 
     soda 

union returns the combined values from Group1 and Group2 with no repetitions. In this case, C is equivalent to the categories of the concatenation, students.

All of the categorical arrays in this example were nonordinal. To combine ordinal categorical arrays, they must have the same sets of categories including their order.