CODEWITHSUNDEEP
iosarraysswift
Usman
Usman

Reputation: 181

How to find first index of an element in array of arrays

I have an array of arrays like

var arr = [[("aa",1),("b",2)],[("c",3),("dd",4)],[("e",5),("f",6)]]

I want to find first index of dd in arr. I am trying this code but failed to get result

let val = arr.first(where: {$0.1 == "dd" })

Upvotes: 0

Views: 870

Answers (5)

Leo Dabus
Leo Dabus

Reputation: 236508

You have an array of arrays. You would need the index of the outer as well as the inner array:

var arr = [[("aa",1),("b",2)],[("c",3),("dd",4)],[("e",5),("f",6)]]

let predicate: ((String,Int)) -> Bool = { $0.0 == "dd" }
if let index = arr.firstIndex(where: {$0.contains(where: predicate)}),
    let subIndex = arr[index].firstIndex(where: predicate) {
    print(arr[index][subIndex])  // ("dd", 4)
}

Expanding on that subject:

extension Collection where Element: Collection {
    func firstIndexAndSubIndex(where predicate: (Element.Element) -> Bool) -> (index: Index, subIndex: Element.Index)? {
        if let index = firstIndex(where: {$0.contains(where: predicate)}),
            let subIndex = self[index].firstIndex(where: predicate) {
            return (index,subIndex)
        }
        return nil
    }
}

usage:

var arr = [[("aa",1),("b",2)],[("c",3),("dd",4)],[("e",5),("f",6)]]

if let idxs = arr.firstIndexAndSubIndex(where: { $0.0 == "dd" } ) {
    print(arr[idxs.index][idxs.subIndex])  // ("dd", 4)
}

Upvotes: 0

MohammadReza Ansari
MohammadReza Ansari

Reputation: 232

You used multi-dimensional arrays, please clarify which index do you looking for(inner/outer index).

In case you mean outer array index:

let outerIndex = arr.firstIndex(where: { $0.contains(where: { $0.0 == "dd"}) })

In case you mean inner array index:

let innerIndex = arr.map({ $0.firstIndex(where: { $0.0 == "dd" }) }).filter({ $0 != nil }).first

In case you need both indexes:

var bothIndex: (outer: Int?, inner: Int?) {
    guard let outerIndex: Int = arr.firstIndex(where: { $0.contains(where: { $0.0 == "dd"}) }) else {
        assertionFailure()
        return (nil,nil)
    }
    
    let innerIndex: Int? = arr[outerIndex].firstIndex(where: { $0.0 == "dd"})
    return (outerIndex, innerIndex)
}

Upvotes: 3

Joakim Danielson
Joakim Danielson

Reputation: 52053

First of all tuples are indexed from 0 so it should be $0.0 and to find an index you need to use firstIndex and lastly, since you have an array of arrays you need to drill down one level and then return when you have a match in an inner array, I use contains for the inner arrays

let val = arr.firstIndex(where: { 
    $0.contains(where: { tuple in tuple.0 == "dd" })
})

Upvotes: 2

Tristan Richard
Tristan Richard

Reputation: 4065

val will be in this case the second inner array. The first inner array that contains "dd"

let val = arr.first(where: { $0.first(where: { $0.0 == "dd" }) != nil } )

Upvotes: 1

Vishvanathan K
Vishvanathan K

Reputation: 9

From the your code, you have an value to each letter like "aa" has 1, "b" has 2, and so on.

If you want to find the value corresponding to "dd", I would suggest you to use Hashmaps/Dictionary !!

So your code will be

   var values = ["aa":1, "b":2, "c":3, "dd":4, "e":5, "f":6]
   let val = values["dd"] //val = 4

Upvotes: 1

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