Indexing

Generalized indexing for Julia

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This package defines functions for getting multiple indices out of dictionaries, tuples, etc, extending this ability beyond AbstractArray.

To acheive this, we introduce new functions and methods:

• getindices(container, indices) - generalizes getindex(container, index) to multiple indices.
• setindices!(container, value, indices) - generalizes setindex!(container, value, index) to multiple indices. The same value is set for each index in indices.
• view(container, indices) - lazy versions of getindices(container, indices) defined for dictionaries.

Quick start

You can install Indexing via Julia's package manager:

julia> using Pkg

julia> Pkg.add("Indexing")

julia> using Indexing

julia> d = Dict(:a => "Alice", :b => "Bob", :c => "Charlie")
Dict{Symbol,String} with 3 entries:
  :a => "Alice"
  :b => "Bob"
  :c => "Charlie"

julia> getindices(d, [:a, :c]) # Preserves type/keys of index collection - an array of length 2
2-element Array{String,1}:
 "Alice"  
 "Charlie"

julia> getindices(d, (:a, :c)) # Preserves type/keys of index collection - a tuple of length 2
("Alice", "Charlie")

julia> getindices(d, Dict("Wife" => :a, "Husband" => :c)) # Preserves type/keys of index collection - a dictionary with keys "Wife" and "Husband"
Dict{String,String} with 2 entries:
  "Wife"    => "Alice"
  "Husband" => "Charlie"

Similarly, view works as a lazy version of getindices, and setindices! works by setting the same value to each specified index.

TODO

This package is a work-in-progress. To complete the package, we need to:

• Performance improvements and propagation of @inbounds annotations.

Future thoughts

Perhaps these could be intergrated into future Julia syntax. One suggestion:

a[i]               --> getindex(a, i)       # scalar only
a.[inds]           --> getindices(a, inds)
a[i] = v           --> setindex!(a, v, i)   # scalar only
a.[inds] = v       --> setindices!(a, v, inds)
a[i] .= v          --> broadcast!(identity, a[i], v)
a.[inds] .= values --> broadcast!(identity, view(a, inds), values)

Note the lack of dotview and maybeview. The last two could support dot-fusion on the RHS. Also, the default for a.[inds] could potentially move to view.