Categorical Arrays

Creating Categorical Arrays

[Example 2-60] Use the categorical function to create a categorical array.

Enter in the Command Window:

S=categorical({'大';'小';'中';'小';'大'})
S =
     大
     小
     中
     小
     大

[Example 2-61] Use the categories function to display categories. Categories are distinguished by unique element values in the categorical array.

Enter in the Command Window:

categories(S)
ans =
    '中'
    '大'
    '小'

[Example 2-62] Use the categorical function to create an ordinal categorical array.

First create a numeric array below:

A=[1 3;2 1;2 3]
A =
     1     3
     2     1
     2     3

Then use the categorical function to convert A to an ordinal categorical array, where 1, 2, and 3 represent the categories '少年' (Youth), '青年' (Young Adult), and '中年' (Middle-aged), respectively.

valueset=[1:3];
catnames={'少年','青年','中年'};
B=categorical(A,valueset,catnames,'Ordinal',true)
B =
     少年      中年
     青年      少年
     青年      中年

Use the iscategorical function to determine if the input is a categorical array, and use the iscategory function to test the categories of a categorical array.

Modifying Categorical Arrays

1. Adding Categories

[Example 2-63] Use the addcats function to add categories to a categorical array. You can add them to the end of the categorical array, or specify a position and add the category before or after that position.

Enter in the Command Window:

A=categorical({'大','小','中';'小','大','小'});
categories(A)
ans =
    '中'
    '大'
    '小'
B=addcats(A, {'很大','微小'});
categories(B)
ans =
    '中'
    '大'
    '小'
    '很大'
    '微小'

[Example 2-64] To demonstrate inserting a category at a specified position, first create an ordinal categorical array.

Enter in the Command Window:

A = categorical({'m' 'l'; 's' 'xl'; 'l' 'm'},{'s' 'm' 'l' 'xl'},'Ordinal',true)
A =
      m      l
      s      xl
      l      m

A is an ordinal categorical array with the specified order s < m < l < xl. Add category xs before category s below.

B=addcats(A, 'xs','Before','s');
categories(B)
ans =
    'xs'
    's'
    'm'
    'l'
    'xl'

2. Setting New Categories

[Example 2-65] Use the setcats function to set new categories for a categorical array.

For the categorical array A below,

A=categorical({'日用品','生鲜','熟食';'熟食','日用品','生鲜'});
A =
     日用品      生鲜       熟食
     熟食       日用品      生鲜
Reset new categories.
B=setcats(A, {'日用品','生鲜','粮油'})
B =
     日用品            生鲜       <undefined>
    <undefined>      日用品      生鲜

Elements in the original categorical array A that are not in the newly specified categories are represented by <undefined>. You can assign values directly, such as:

B(1,3)= '粮油';
B(2,1)= '粮油';
B(2,1)= '粮油';
B
B =
     日用品      生鲜       粮油
     粮油       日用品      生鲜

3. Merging Categories

[Example 2-66] Use the mergecats function to merge categories. You can also specify multiple categories to merge, merging them into the first category, or specify a new name for the merged category.

Enter in the Command Window:

A = categorical({'red';'blue';'pink';'red';'blue';'pink'});

Merge categories 'red' and 'pink' in categorical array A into 'red'.

B=mergecats(A,{ 'red','pink'})
B =
     red
     blue
     red
     red
     blue
     red

You can also specify a new name for the merged category.

B=mergecats(A,{ 'red','pink'}, '红色')
B =
     红色
     blue
     红色
     红色
     blue
     红色

4. Removing Categories

[Example 2-67] Use the removecats function to remove unused categories or specified categories.

For the categorical array A below, 3 categories are defined, but only two categories are used in the array elements.

A = categorical({'red';'blue';'blue';'red';'blue';'red'},{'red','blue';'pink'});
categories(A)
ans =
    'red'
    'blue'
    'pink'

Use the removecats function to remove the unused 'pink' category.

B=removecats(A)
ans =
    'red'
    'blue'

You can also specify the 'pink' category to remove.

B=removecats(A, 'pink');