Handling categorical data
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This tutorial follows loosely the docs.
using CategoricalArrays
v = categorical(["AA", "BB", "CC", "AA", "BB", "CC"])6-element CategoricalArrays.CategoricalArray{String,1,UInt32}:
"AA"
"BB"
"CC"
"AA"
"BB"
"CC"This declares a categorical vector, i.e. a Vector whose entries are expected to represent a group or category. You can retrieve the group labels using levels:
levels(v)3-element Vector{String}:
"AA"
"BB"
"CC"which, by default, returns the labels in lexicographic order.
You can specify that categories are ordered by specifying ordered=true, the order then follows that of the levels. If you wish to change that order, you need to use the levels! function. Let's see two examples.
v = categorical([1, 2, 3, 1, 2, 3, 1, 2, 3], ordered=true)
levels(v)3-element Vector{Int64}:
1
2
3Here the lexicographic order matches what we want so no need to change it, since we've specified that the categories are ordered we can do:
v[1] < v[2]trueLet's now consider another example
v = categorical(["high", "med", "low", "high", "med", "low"], ordered=true)
levels(v)3-element Vector{String}:
"high"
"low"
"med"The levels follow the lexicographic order which is not what we want:
v[1] < v[2]trueIn order to re-specify the order we need to use levels!:
levels!(v, ["low", "med", "high"])6-element CategoricalArrays.CategoricalArray{String,1,UInt32}:
"high"
"med"
"low"
"high"
"med"
"low"now things are properly ordered:
v[1] < v[2]false
You can also have a categorical vector with missing values:
v = categorical(["AA", "BB", missing, "AA", "BB", "CC"]);that doesn't change the levels:
levels(v)3-element Vector{String}:
"AA"
"BB"
"CC"