They're asking you to give the _ variable a name, and it's entirely up to you what you call it; it's just a variable name.
The right-hand side was already given a name, numbers, and it represents the right-hand side of the information in the interestingNumbers array, i.e. the arrays of numbers.
The underscore represents the left-hand side of the data, i.e. the three String values: Prime, Fibonacci, and Square.
If you do this, you should see how it works:
let interestingNumbers = [
"Prime": [2, 3, 5, 7, 11, 13],
"Fibonacci": [1, 1, 2, 3, 5, 8],
"Square": [1, 4, 9, 16, 25]
]
var largest = 0
var largestSet = ""
for (dataset, numbers) in interestingNumbers {
for number in numbers {
if number > largest {
largest = number
largestSet = dataset
}
}
}
print ("largestSet '\(largestSet)' with value: \(largest)")
Topic:
Programming Languages
SubTopic:
Swift