Julia: Passing Dict items as arguments to a function

5
votes

I am trying to pass a Dict to a function in Julia. The Dict contains pairs of argument names and their respective values. Let's say I have a function f and a Dict d:

julia> function f(x=10, y=10, z=10); return x^2, y^2, z^2; end
julia> d = Dict("x"=>3, "z"=>7, "y"=>5)

This throws a MethodError:

julia> f(d...)
ERROR: MethodError: no method matching ^(::Pair{String,Int64}, ::Int64)

I also tried using a NamedTuple, but this seems useless as it is sensitive to the order of the elements in the tuple and doesn't match their names with the function argument names:

julia> t = (x=3, z=7, y=5)
julia> f(t...)
(9, 49, 25)

I am sure there is a way to do this. Am trying to do this with the wrong types? In python, what I am looking for would look like this:

>>> def f(x=10, y=10, z=10):
...     return x**2, y**2, z**2
>>> d = {'x':3, 'z':7, 'y':5}
>>> f(**d)
(9, 25, 49)
2
pythonfunctionargumentsjulia

2 Answers

16
votes

Firstly, since you want the names of the arguments to be important (keyword arguments) you need to use a ; in the function definition:

f(;x=10, y=10, z=10) = x^2, y^2, z^2

Secondly, you should use a dictionary where the keys are Symbols:

d = Dict(:x=>3, :z=>7, :y=>5)

And thirdly, you want to indicate that you are splatting keyword arguments by splatting after ;:

f(;d...)
# giving the result (9, 25, 49)
0
votes

It seems that you need to square all values of a dictionary. use comprehension maybe a better solution.

d = Dict(:x=>3, :z=>7, :y=>5)
[println(p.first, "=> ", p.second^2) for p in  d];

In the above, p.first will get the keys, while p.second will get values of the dictionary.