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Dictionaries
Removing Elements

There are several options for removing key-value pairs from a Swift dictionary.

In Swift, the keyword nil describes something as being empty or having no value. If we were to set the value of a key to nil, the key-value pair would be removed from the dictionary:

dictionaryName[Key] = nil

Consider the following dictionary bookShelf that stores key-value pairs of titles and authors for books we currently own:

var bookShelf = [ "Goodnight Moon": "Margaret Wise Brown", "The BFG": "Roald Dahl", "Falling Up": "Shel Silverstein" ]

Imagine being part of a book drive and donating one of the books. To keep bookShelf accurate, let’s remove the key-value pair "The BFG": "Roald Dahl" by setting the value of "The BFG" to nil:

bookShelf["The BFG"] = nil

We can also remove a single key-value pair using the .removeValue() method:

dictionaryName.removeValue(forKey: Key)

The .removeValue() method takes a name of a key after forKey: to know which key-value pair to remove.

If we were to use the .removeValue() method to delete an element from bookShelf, our code would look like this:

bookShelf.removeValue(forKey: "The BFG")

If we wanted to delete every key-value pair in a dictionary at once, we could use the .removeAll() method:

dictionaryName.removeAll()

Note how this method does not take any parameters; simply append .removeAll() to an existing dictionary.

If we needed to remove all the values in bookShelf, our syntax would be:

bookShelf.removeAll()

Instructions

1.

Check out the dictionary rainbowHex in Color.swift. The dictionary should only contain the names and hex values for the colors of the rainbow, but it currently has a few extra elements.

Remove the key-value pair "maroon": "#800000" from rainbowHex using nil.

2.

Remove the key-value pair "pink": "#ffc0cb" from rainbowHex using the .removeValue() method.

3.

Remove all the elements from rainbowHex using .removeAll().

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