How to Perform One-Hot Encoding in Julia Flux
Overview
One-hot encoding is the process of mapping data to standard basis vectors based on its classification. Flux provides functions for this.
Code1
onehot()
onehot(x, labels, [default])
Returns x .== labels
. However, it does not return the exact same result, but returns a type called OneHotVector
. For encoding multiple data points, use onehotbatch()
below.
julia> 3 .== [1,3,4]
3-element BitVector:
0
1
0
julia> Flux.onehot(3, [1,3,4])
3-element OneHotVector(::UInt32) with eltype Bool:
⋅
1
⋅
julia> Flux.onehot(3, 1:6)
6-element OneHotVector(::UInt32) with eltype Bool:
⋅
⋅
1
⋅
⋅
⋅
julia> Flux.onehot(:c, [:a,:b,:c])
3-element OneHotVector(::UInt32) with eltype Bool:
⋅
⋅
1
If a default value is specified, elements not in the labels are labeled with the default value.
julia> Flux.onehot(5, [1,2,3], 3)
3-element OneHotVector(::UInt32) with eltype Bool:
⋅
⋅
1
onehotbatch()
onehotbatch(xs, labels, [default])
Used for encoding multiple data points at once. The usage is the same as onehot()
.
julia> Flux.onehotbatch([1,2,5], [1,2,3], 3)
3×3 OneHotMatrix(::Vector{UInt32}) with eltype Bool:
1 ⋅ ⋅
⋅ 1 ⋅
⋅ ⋅ 1
julia> Flux.onehotbatch(['a', 'b', 'c', 'h'], 'a':'c', 'c')
3×4 OneHotMatrix(::Vector{UInt32}) with eltype Bool:
1 ⋅ ⋅ ⋅
⋅ 1 ⋅ ⋅
⋅ ⋅ 1 1
onecold()
onecold(y::AbstractArray, labels = 1:size(y,1))
This is the reverse operation of onehot()
, onehotbatch()
. It decodes the one-hot encoding. It can be used even if the input is not a OneHotVector
.
julia> x1 = Flux.onehot(2, 1:3)
3-element OneHotVector(::UInt32) with eltype Bool:
⋅
1
⋅
julia> Flux.onecold(x1)
2
julia> x2 = Flux.onehot('a', ['a', 'b', 'c'])
3-element OneHotVector(::UInt32) with eltype Bool:
1
⋅
⋅
julia> Flux.onecold(x2, 'a':'c')
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
julia> Flux.onecold([0.1, 0.2, 0.5], [:a, :b, :c])
:c
3×3 OneHotMatrix(::Vector{UInt32}) with eltype Bool:
1 ⋅ ⋅
⋅ 1 ⋅
⋅ ⋅ 1
julia> x3 = Flux.onehotbatch([1,2,5], [1,2,3], 3)
3×3 OneHotMatrix(::Vector{UInt32}) with eltype Bool:
1 ⋅ ⋅
⋅ 1 ⋅
⋅ ⋅ 1
julia> Flux.onecold(x3)
3-element Vector{Int64}:
1
2
3
Environment
- OS: Windows10
- Version: Julia 1.7.1, Flux 0.12.8