Return an array of index values from array of Bool where true

Question

Anyone know an elegant way to return an array of index values from an array of Bools where the values are true. E.g:

let boolArray = [true, true, false, true]

This should return:

[0,1,3]

stackoverflow.com/questions/24041842/… ?

Larme
– Larme

2016-07-06 13:24:35 +00:00
Commented Jul 6, 2016 at 13:24 — Larme
– Larme, Commented Jul 6, 2016 at 13:24

dfrib · Accepted Answer · 2016-07-06 13:25:30Z

7

let boolArray = [true, true, false, true]
let trueIdxs = boolArray.enumerate().flatMap { $1 ? $0 : nil }
print(trueIdxs) // [0, 1, 3]

Alternatively (possibly more readable)

let boolArray = [true, true, false, true]
let trueIdxs = boolArray.enumerate().filter { $1 }.map { $0.0 }
print(trueIdxs) // [0, 1, 3]

edited Jul 6, 2016 at 13:25

answered Jul 6, 2016 at 13:23

dfrib

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5 Comments

Jeet Over a year ago

Would you also please explain why you think it is elegant and best approach in your opinion that would be a great help.

dfrib Over a year ago

@JeetendraChoudhary When we mention "elegant" in questions regarding Swift, I, among many, turn to the functional approaches available in Swift. There's numerous different approaches to accessing the indices that uphold some given condition w.r.t. the values of an array. I personally use the enumerate().flatMap or enumerate().filter{ ... }.map approach myself.

Jeet Over a year ago

Thank you indeed very helpful, It always helps to learn from seniors like you what and why they like certain approach or method. Thank you once again.

dfrib Over a year ago

@JeetendraChoudhary happy to help!

Danny Over a year ago

Awesome. Thanks @dfri

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