MATLAB Programming Fundamentals - MathWorks

Advantages of Using Categorical Arrays

In this section...

“Natural Representation of Categorical Data” on page 8-43

“Mathematical Ordering for Character Vectors” on page 8-43

“Reduce Memory Requirements” on page 8-43

Natural Representation of Categorical Data

categorical is a data type to store data with values from a finite set of discrete

categories. One common alternative to using categorical arrays is to use character arrays

or cell arrays of character vectors. To compare values in character arrays and cell arrays

of character vectors, you must use strcmp which can be cumbersome. With categorical

arrays, you can use the logical operator eq (==) to compare elements in the same way

that you compare numeric arrays. The other common alternative to using categorical

arrays is to store categorical data using integers in numeric arrays. Using numeric arrays

loses all the useful descriptive information from the category names, and also tends to

suggest that the integer values have their usual numeric meaning, which, for categorical

data, they do not.

Mathematical Ordering for Character Vectors

Categorical arrays are convenient and memory efficient containers for nonnumeric data

with values from a finite set of discrete categories. They are especially useful when the

categories have a meaningful mathematical ordering, such as an array with entries from

the discrete set of categories {'small','medium','large'} where small < medium

< large.

An ordering other than alphabetical order is not possible with character arrays or cell

arrays of character vectors. Thus, inequality comparisons, such as greater and less than,

are not possible. With categorical arrays, you can use relational operations to test for

equality and perform element-wise comparisons that have a meaningful mathematical

ordering.

Reduce Memory Requirements

This example shows how to compare the memory required to store data as a cell array of

character vectors versus a categorical array. Categorical arrays have categories that are

Advantages of Using Categorical Arrays