MATLAB Programming Fundamentals - MathWorks

Access Data Using Categorical Arrays

In this section...

“Select Data By Category” on page 8-30

“Common Ways to Access Data Using Categorical Arrays” on page 8-30

Select Data By Category

Selecting data based on its values is often useful. This type of data selection can involve

creating a logical vector based on values in one variable, and then using that logical

vector to select a subset of values in other variables. You can create a logical vector for

selecting data by finding values in a numeric array that fall within a certain range.

Additionally, you can create the logical vector by finding specific discrete values. When

using categorical arrays, you can easily:

• Select elements from particular categories. For categorical arrays, use the logical
  operators == or ~= to select data that is in, or not in, a particular category. To select
  data in a particular group of categories, use the ismember function.

For ordinal categorical arrays, use inequalities >, >=, <, or <= to find data in

categories above or below a particular category.

• Delete data that is in a particular category. Use logical operators to include or
  exclude data from particular categories.


• Find elements that are not in a defined category. Categorical arrays indicate
  which elements do not belong to a defined category by . Use the
  isundefined function to find observations without a defined value.

Common Ways to Access Data Using Categorical Arrays

This example shows how to index and search using categorical arrays. You can access

data using categorical arrays stored within a table in a similar manner.

Load Sample Data

Load sample data gathered from 100 patients.

load patients

whos

8 Categorical Arrays