Let's say I have an array of dictionaries, and each contains an array of letters. Like this:
let dicts = [["letters" : ["a","b","c"]],
["letters" : ["d","e","f"]]]
What is the most efficient way to create a flattened array of all the letters from all the dictionaries?
You can use reduce(_:_:) for that.
let array = dicts.reduce([]) { $0 + ($1["letters"] ?? []) }
print(array) // ["a","b","c","d","e","f"]
Edit: As @Hamish suggested a link in comment simplest solution is having less time, so if you are having large amount of data then you can use forEach closure with array.
var result = [String]()
dicts.forEach {
result.append(contentsOf: $0["letters"] ?? [])
}
{ $0 + ($1["letters"] as? [String] ?? []) }
You can use flatMap() to map each dictionary to the corresponding
letters array and join the results:
let dicts = [["letters" : ["a","b","c"]],
["letters" : ["d","e","f"]]]
let letters = Array(dicts.flatMap { $0["letters"] }.joined())
print(letters) // ["a", "b", "c", "d", "e", "f"]
This is effective insofar as no additional intermediate arrays are
created during the join. As @Hamish pointed out below, the
intermediate [[String]] can be avoided with
let letters = Array(dicts.lazy.flatMap { $0["letters"] }.joined())
[[String]] with Array(dicts.lazy.flatMap { $0["letters"] }.joined()) :)
for _ in 1...10 { <your do blocks> }) ?You can use any one of these. You don't need to specify the key name of the dictionary.
Solution 1
let array = dicts.reduce([]) { $0 + ($1.values.reduce([]) { $0 + $1 }) }
print(array) // ["a","b","c","d","e","f"]
Solution 2
let array = dicts.flatMap { $0.values.joined() }
print(array) // ["a","b","c","d","e","f"]
