How can I add a new key value pair to an existing dictionary?

Question

I have some dictionary that already exists. I want to add a new key-value pair, but I do not want to create a new dictionary from scratch.

How can I add a new key-value pair to an existing dictionary in Julia?

Answer 1

Julia uses the common dict[key] = value syntax for setting a key-value pair:

julia> dict = Dict(1 => "one")
Dict{Int64,String} with 1 entry:
  1 => "one"

julia> dict[2] = "two"
"two"

julia> dict
Dict{Int64,String} with 2 entries:
  2 => "two"
  1 => "one"

The same syntax will override a key-value pair if the key already exists:

julia> dict
Dict{Int64,String} with 2 entries:
  2 => "two"
  1 => "one"

julia> dict[1] = "foo"
"foo"

julia> dict
Dict{Int64,String} with 2 entries:
  2 => "two"
  1 => "foo"

dict[key] = value is syntax for a setindex! call. Although not as common, you can call setindex! directly:

julia> dict = Dict(1 => "one")
Dict{Int64,String} with 1 entry:
  1 => "one"

julia> setindex!(dict, "two", 2)
Dict{Int64,String} with 2 entries:
  2 => "two"
  1 => "one"