Create a categorical array containing various colors.

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

A = 6x1 categorical
     red 
     blue 
     pink 
     red 
     blue 
     red 

A is a 6-by-1 categorical array.

Display the categories of A.

categories(A)

ans = 3x1 cell
    {'blue'}
    {'pink'}
    {'red' }

The three categories are in alphabetical order.

Merge the categories red and pink into the category red. Specify red first in oldcats to use it as the merged category.

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

B = 6x1 categorical
     red 
     blue 
     red 
     red 
     blue 
     red 

mergecats replaces the value pink from A(3) with red.

Display the categories of B.

categories(B)

ans = 2x1 cell
    {'blue'}
    {'red' }

B has two categories instead of three.

Create a categorical array containing various items.

A = categorical({'shirt' 'pants'; 'shoes' 'shirt'; 'dress' 'belt'})

A = 3x2 categorical
     shirt      pants 
     shoes      shirt 
     dress      belt  

Display the categories of A.

categories(A)

ans = 5x1 cell
    {'belt' }
    {'dress'}
    {'pants'}
    {'shirt'}
    {'shoes'}

The five categories are in alphabetical order.

Merge the categories belt and shoes into a new category called other.

B = mergecats(A,{'belt' 'shoes'},'other')

B = 3x2 categorical
     shirt      pants 
     other      shirt 
     dress      other 

The value other replaces all instances of belt and shoes.

Display the categories of B.

categories(B)

ans = 4x1 cell
    {'other'}
    {'dress'}
    {'pants'}
    {'shirt'}

B has four categories and the order is no longer alphabetical. other appears in place of belt.

Create an ordinal categorical array.

A = categorical([1 2 3 2 1],1:3,{'poor','fair','good'},'Ordinal',true)

A = 1x5 categorical
     poor      fair      good      fair      poor 

Display the categories of A.

categories(A)

ans = 3x1 cell
    {'poor'}
    {'fair'}
    {'good'}

Since A is ordinal, the categories have the mathematical ordering poor < fair < good.

Consider all fair or poor values to be bad. Since A is ordinal, the categories to merge must be consecutive.

B = mergecats(A,{'fair' 'poor'},'bad')

B = 1x5 categorical
     bad      bad      good      bad      bad 

The value bad replaces all instances of fair and poor.

Display the categories of B.

categories(B)

ans = 2x1 cell
    {'bad' }
    {'good'}

B has two categories with the mathematical ordering: bad < good.