map, filter, reduce in Swift

The functional trio, plus compactMap for the misses.

let legTimes = [512.0, 448.5, 630.0, 505.25]

// map transforms, filter keeps, reduce folds.
let minutes = legTimes.map { $0 / 60 }
print(minutes)

let quickLegs = legTimes.filter { $0 < 520 }
print("Quick legs: \(quickLegs.count)")

let total = legTimes.reduce(0, +)
print("Race time: \(total) s")

// compactMap drops the misses while transforming.
let logged = ["512", "n/a", "448"]
let parsed = logged.compactMap { Double($0) }
print("Parsed \(parsed.count) of \(logged.count)")

How it works

1. map transforms every element into a new array.
2. filter keeps by predicate; reduce(0, +) folds.
3. compactMap { Double($0) } transforms and drops the nils.

Keywords and builtins used here

• Double
• count
• filter
• let
• map
• print
• reduce

The run, in numbers

Lines

16

Characters to type

482

Tokens

119

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 102 seconds.

Type this snippet

Step 3 of 3 in Functions & closures, step 9 of 27 in Language basics.

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map, filter, reduce in other languages

• Julia