How to determine if a dictionary has some key?

Question

I want to key into a dictionary, but Julia throws an exception if the key does not exist. To avoid the exception, I first have to check if they key exists in the dictionary.

I'm using this custom function for now:

function has_some_key(dict, key)
   for (k, v) in dict
       if k == key
           return true
       end
   end
   return false
end

Is there a better way to determine if a dictionary has a mapping for a given key?

Answer 1

haskey will check whether some collection has a mapping for a given key:

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

julia> haskey(d, 1)
true

julia> haskey(d, 3)
false

Answer 2

Another way, which might be viable depending on your use case, is to use get to provide a default value in case the key is not present:

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

julia> get(d, 1, "zero")
"one"

julia> get(d, 3, "zero")
"zero"

There's also get!, which will store the default value for the queried key as well.