Remove elements from Array of Array Swift

Question

For context I'm creating my own hashmap in swift.

I've got an element and I'm storing the elements in buckets which is an array of arrays

struct Element {
    var key: Int
    var value: Int
}

class MyHashMap {
    var buckets : [[Element]] = [[]]

    init() {
        buckets = [Array(repeating: Element(key: -1, value: -1), count: 2)]
        buckets.append([Element(key: 3, value: 4)])
    }

}

I want to remove all the buckets where the key is -1 and I'm struggling.

Flatmap does not return the right type i.e.

hashmap.buckets.flatMap{$0}.filter{$0.key != -1}

is incorrect.

How can I remove all of the buckets with key -1?

If any of the answers has solved your issue then please mark it as accepted or give some feedback why this isn't resolved yet. — Joakim Danielson
– Joakim Danielson, Commented Jun 1, 2019 at 7:14

Martin R · Accepted Answer · 2019-05-27 08:01:52Z

1

Map the outer array to a new array of arrays, where from the inner array only the elements with key != -1 are preserved. I would make this a method of the MyHashMap class:

class MyHashMap {
    // ...

    func compactBuckets() {
        buckets = buckets.map { $0.filter { $0.key != -1 }}
    }
}

Alternatively (and possibly more efficient), with a loop over the indices of the outer array:

    func compactBuckets() {
        for i in buckets.indices {
            buckets[i].removeAll(where: { $0.key == -1 })
        }
    }

In either case you may additionally want to remove empty inner arrays from the outer array:

        buckets.removeAll(where: { $0.isEmpty })

edited May 27, 2019 at 8:01

answered May 27, 2019 at 7:50

Martin R

541k98 gold badges1.3k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Joakim Danielson Over a year ago

Doing print(hashmap.buckets.count) after either of your suggestions will return 2 instead of 1. There seems to be an empty array left in the buckets array. Notice what it says in the question "I want to remove all the buckets where the key is -1"

Martin R Over a year ago

@JoakimDanielson: I interpreted the problem as “remove all entries with key=-1 from the nested array,” not as “remove all inner arrays which have any entry with key=-1,” but I may be wrong of course. – You were right about the first point.

Joakim Danielson Over a year ago

Hopefully OP will let us know which interpretation is right.

WishIHadThreeGuns Over a year ago

It's a hashmap. Therefore remove all entries with key=-1

Joakim Danielson · Accepted Answer · 2019-05-27 07:41:52Z

0

You can use removeAll where you filter with contains for the buckets

hashmap.buckets.removeAll { $0.contains { $0.key == -1 } }

answered May 27, 2019 at 7:41

Joakim Danielson

53k5 gold badges36 silver badges79 bronze badges

Collectives™ on Stack Overflow

Remove elements from Array of Array Swift

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related