A pooled representation of arrays for purposes of compression when there are few unique elements.
Installation: at the Julia REPL, import Pkg; Pkg.add("PooledArrays")
Usage:
Working with PooledArray objects does not differ from working with general
AbstractArray objects, with two exceptions:
- If you hold mutable objects in
PooledArrayit is not allowed to modify them after they are stored in it. - In multi-threaded context it is not safe to assign values that are not already
present in a
PooledArray's pool from one thread while either reading or writing to the same array from another thread.
Keeping in mind these two restrictions, as a user, the only thing you need to
learn is how to create PooledArray objects. This is accomplished by passing
an AbstractArray to the PooledArray constructor:
julia> using PooledArrays
julia> PooledArray(["a" "b"; "c" "d"])
2×2 PooledMatrix{String, UInt32, Matrix{UInt32}}:
"a" "b"
"c" "d"
PooledArray performs compression by storing an array of reference integers and
a mapping from integers to its elements in a dictionary. In this way, if the
size of the reference integer is smaller than the size of the actual elements
the resulting PooledArray has a smaller memory footprint than the equivalent
Array. By default UInt32 is used as a type of reference integers. However,
you can specify the reference integer type you want to use by passing it as a
second argument to the constructor. This is usually done when you know that you
will have only a few unique elements in the PooledArray.
julia> PooledArray(["a", "b", "c", "d"], UInt8)
4-element PooledVector{String, UInt8, Vector{UInt8}}:
"a"
"b"
"c"
"d"
Alternatively you can pass the compress and signed keyword arguments to the
PooledArray constructor to automatically select the reference integer type.
When you pass compress=true then the reference integer type is chosen to be
the smallest type that is large enough to hold all unique values in array. When
you pass signed=true the reference type is signed (by default it is unsigned).
julia> PooledArray(["a", "b", "c", "d"]; compress=true, signed=true)
4-element PooledVector{String, Int8, Vector{Int8}}:
"a"
"b"
"c"
"d"
Maintenance: PooledArrays is maintained collectively by the JuliaData collaborators. Responsiveness to pull requests and issues can vary, depending on the availability of key collaborators.