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iOS Swift Closures Closures and Closure Expressions Using Filter

Beating the odds

I'm stuck! This works when I tried it in Playground, but not here.

let numbers = [Int](0...50)

let isOdd = numbers.map({(i: Int) -> Bool in return ((i % 2) - 1 ) == 0})

2 Answers

Martin Wildfeuer
Martin Wildfeuer
Courses Plus Student 11,071 Points

Hey Beth!

Define a function, named isOdd, to check if a number is odd. The function takes a number and returns either true or false depending on if the number is odd or not.

You need to create a function first. This function takes an Int and returns a Bool. In the body, we check whether a number is odd and return the boolean result. Your approach with (i % 2) - 1 ) == 0 is really clever, btw! To "invert" the result, you can also use the != "not equal" operator, which is easier to read.

func isOdd(i: Int) -> Bool {
  return i % 2 != 0

Given an array of integers, called numbers, use the filter function (and the helper function we created) to create a new array containing only odd numbers. Assign this new array to a constant named oddNumbers.

Make sure to use the filter function instead of map, as stated above.

let oddNumbers = numbers.filter(isOdd)

Hope that helps!

Thank you! That makes a lot more sense.