CODEWITHSUNDEEP
juliamultiple-dispatch
Owen
Owen

Reputation: 466

Julia: Unpack Arguments from Dictionary or Array for Functions with Multiple Dispatch

My question originated where I had a dictionary of DataFrame values (with compatible columns), and I want to vcat them all together.

Consider how the string function can take any number of string arguments: string("Fish ", "and ", "chips ") == "Fish and chips " (is true). I have a dictionary myLunch = Dict(:a => "Fish ", :b => "and ", :c => "chips ") and I want to unpack the dictionary and pass its values to string as though they were arguments.

string( unpack(myLunch)) == "Fish and chips "

Analogously, my data might be stored in an array, lunch = ["Fish ", "and ", "chips "], and I want to pass the array's contents as arguments:

string( unpack(lunch) )

How can you do this?

Here is a related post on StackOverflow for tuples

Upvotes: 1

Views: 715

Answers (1)

BatWannaBe
BatWannaBe

Reputation: 4510

First a little renaming for clarity:

luncharray = ["Fish ", "and ", "chips "]
lunchdict = Dict(:a => "Fish ", :b => "and ", :c => "chips ")

For an array, you just splat it into several arguments, just like you could for a tuple:

string(luncharray...)

Dictionaries are key-value pairs, and you can iterate over its values. You can splat any iterable into several arguments:

# don't care about order
       # only need values of Dict
string(values(lunchdict)...)

The problem with the dictionary is that it doesn't preserve an order like arrays do; you can't even count on insertion order. It's possible to get something like and Chips Fish . Therefore, we have to sort it ourselves. Coincidentally, ["Fish", "and", "Chips"] is already in order, but we usually don't want to sort by words. Your keys are :a, :b, :c to indicate order, so lets sort by that.

# care about order
        # value from key   # sort an array of keys in the Dict
string((lunchdict[key] for key in sort(collect(keys(lunchdict))))...)

Upvotes: 4

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