How to use reduce() to condense an array into a single value

Paul Hudson    February 12th 2018    @twostraws

The reduce() method iterates over all items in array, combining them together somehow until you end up with a single value. The “somehow” is specified by a closure you provide, for example you might want to count how many characters are provided in an array of names, which looks like this:

let names = ["Taylor", "Paul", "Adele"]
let count = names.reduce(0) { $0 + $1.count }
print(count)

That starts with a total of 0 (the parameter passed in to reduce(), then adds that to the count of each string in the array. So, it starts by adding 6 for Taylor (so the running total is 6), then adds 4 for Paul (so the running total is 10), then adds 5 more for Adele (so the running total is 15.)

Available from iOS – learn more in my book Pro Swift

Did this solution work for you? Please pass it on!

Tweet

Other people are reading…

• How to check whether a date is inside a date range
• What’s the difference between a static variable and a class variable?
• How to use typealias to make it easier to use complex types
• Using stride() to loop over a range of numbers
• What is a closure?

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.