Tools for working with categorical variables, including ordered categories (AKA ordinal variables). This package is intentionally designed to provide low-level machinery for working with categorical data. Most of API would not be of interest to end-users, only those working on higher-level projects like DataArrays.jl.

Examples

Suppose that you want to work with three categories. To represent information about those categories, you first build a pool that enumerates the possible categories:

using CategoricalData

pool = CategoricalPool(["Group A", "Group B", "Group C"])

To create a specific observation, you create a CategoricalVariable object that points to the pool's internal index of values:

cv = CategoricalVariable(1, pool)

If you know that you're working with ordinal data, you can use an OrdinalPool object, which augments a CategoricalPool with an ordering:

opool = OrdinalPool(
    ["Group A", "Group B", "Group C"],
    ["Group B", "Group C", "Group A"]
)

In this example, the first argument to OrdinalPool specifies the possible levels that this ordered factor can take on. The second argument provides the levels of the factors in their sorted order.

Once an OrdinalPool exists, you can define OrdinalVariable objects and compare their position in the order:

ov1 = OrdinalVariable(1, opool)
ov2 = OrdinalVariable(2, opool)

ov1 < ov2
ov1 > ov2

Full API

As shown above, there are constructors for:

• CategoricalPool
• CategoricalVariable
• OrdinalPool
• OrdinalVariable

There are also methods for accessing and manipulating the pool:

• levels: Determine which levels a pool allows
• levels!: Reset, en masse, the levels that a pool allows
• add!: Add one or more levels to the pool
• delete!: Delete one or more levels from the pool
• order: Determine the order of an ordinal pool
• order!: Reset, en masse, the ordering of an ordinal pool

Note that add! and delete! do not work on ordinal variables because they not provide any mechanism for specifying how the changes to the levels affect the ordering of the pool.