For example say I have an array like so:
var someArray = ["1", "1", "2"]
I need to put this into two arrays that look like:
["1","1"]
["2"]
How can I go about this?
Any help would be great!
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3 Answers
Use Dictionary initializer init(grouping:by:) Then just get arrays by accessing values property.
Example:
let dic = Dictionary(grouping: someArray) { $0 }
let values = Array(dic.values)
print(values)
Result:
[["2"], ["1", "1"]]
8 Comments
Robert D. Mogos
This is the best way. He's using O(N) runtime complexity to match the objects compared to @Bruno 's implementation which uses O(N*N)
Robert D. Mogos
@kirander remove
.first!. If he's working with Strings, first would group numbers like "1" and "12" together
Fogmeister
My initial down vote was due to it being a link only post. Now this is definitely my favourite method :D
farhan
on the first line, i get an error
Generic parameter 'key' could not be inferredRobert D. Mogos
Show us how you declared the array
|
Here are some facts (the upvote and answer should go to @kirander)
With @kirander method's is using the Dictionary to map the objects in a O(N) runtime and O(N) memory.
The other solutions are mostly running in O(N*N) runtime and O(N) memory. Because of this, grouping a random array of 1000 items will take: 0.07s with @kirander solution and 34s. with other solutions.
func benchmark(_ title:String, code: ()->()) {
let startTime = CFAbsoluteTimeGetCurrent()
code()
let timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
print("Time elapsed for \(title): \(timeElapsed) s.")
}
var array:[String] = []
for _ in 0...1000 {
array.append("\(Int(arc4random_uniform(10)))")
}
// @kirander solution 0.07s
benchmark("Dictionary", code: {
let dic = Dictionary(grouping: array, by: { $0 })
let values = Array(dic.values)
})
// @Bruno solution ~34s
benchmark("Array", code: {
var resultingArrays = [[String]]()
for value in array {
let ar = array.filter({ $0 == value })
if !resultingArrays.contains(where: {$0 == ar}) {
resultingArrays.append(ar)
}
}
})
You could try something like this:
var someArray = ["1", "1", "2"]
var resultingArrays = [[String]]()
for value in someArray {
let array = someArray.filter({ $0 == value })
if !resultingArrays.contains(where: {$0 == array}) {
resultingArrays.append(array)
}
}
2 Comments
Bruno
@kirander's comment was edited. Now I agree that his answer is the more efficient and better one.
Ashok Londhe
@RobertD.Mogos Its my opinion you may have different opinion. Because when i commented on this answer that time no one given proper answer. So according to me it is best answer.