adding dictionaries in Julia by summing values of same keys

Question

I have two dictionaries a1 and a2 in Julia.

a1 = {"A"=>1, "B"=>2}
a2 = {"A"=>4, "B"=>1, "C"=>3}

I would like to combine it to get this.

final={"A"=>5, "B"=>3, "C"=>3}

In Python, I convert the dictionary to collection counter and combine them together.

Answer 1

Have a look at DataStructures.jl counter.

julia> using DataStructures: counter

julia> a1 = Dict{ASCIIString, Int64}("A"=>1, "B"=>2)
Dict{ASCIIString,Int64} with 2 entries:
  "B" => 2
  "A" => 1

julia> a2 = Dict{ASCIIString, Int64}("A"=>4, "B"=>1, "C"=>3)
Dict{ASCIIString,Int64} with 3 entries:
  "B" => 1
  "A" => 4
  "C" => 3

julia> merge(counter(a1), counter(a2)).map
Dict{ASCIIString,Int64} with 3 entries:
  "B" => 3
  "A" => 5
  "C" => 3

Answer 2

For anyone looking at this now, counter is no longer necessary -- use merge(+, a1, a2).

julia> a1 = Dict("A"=>1, "B"=>2)
Dict{String,Int64} with 2 entries:
  "B" => 2
  "A" => 1
julia> a2 = Dict("A"=>4, "B"=>1, "C"=>3)
Dict{String,Int64} with 3 entries:
  "B" => 1
  "A" => 4
  "C" => 3
julia> merge(+, a1, a2)
Dict{String,Int64} with 3 entries:
  "B" => 3
  "A" => 5
  "C" => 3