Updating a string quantity in an array in Swift - arrays

Question

Let's say I have an array of strings:
var array: [String] = ["a", "a", "b", "c", "c", "c", "d", "d"]
In the array, I have 4 times a, 1 time b, 3 times c and 2 times d.
I want to update the a value from 4 to 7, and the c value from 3 to 1.
The maximum times I want a single string to be in the array is up to 10 times.
I tried to do it using this:
for _ in 0..<10 {
if array.contains("a") {
if let index = array.index(of: "a") {
array.remove(at: index)
}
}
}
for _ in 0..<7 {
array += ["a"]
}
First, in a loop which runs 10 times, I check every time if the array still contains a, and if so then I remove it. After that, I run a loop for 7 times, and this loop adds every time another a value to the array, until there are supposed to be 7 a in the array.
This isn't what's really happening. What really happening is that it replaces all objects in the array to a, and definitely runs more than 7 times.
What can I do to solve it?

Answer 1

I would suggest using a dictionary. This current method is not really efficient.
var dict = [
"a": 4,
"b": 8
]
This way you can update the value for each letter without having to repeat them in an array. To set a dictionary value you can use the subscript:
dict["a"] = 2
This seems more suited to what you're trying to do.

Answer 2

If you want to bring the occurrences of a given element to n you can write something like this.
extension Array where Element == String {
func updated(numOccurrencies: Int, ofWord word: String) -> [String] {
let currentOccurrencies = self.filter { $0 == word }.count
let delta = numOccurrencies - currentOccurrencies
if delta > 0 {
let newOccurrencies = Array<String>(repeatElement(word, count: delta))
return self + newOccurrencies
}
if delta < 0 {
var numElmsToDelete = -delta
return filter {
guard $0 == word else { return true }
guard numElmsToDelete > 0 else { return true }
numElmsToDelete -= 1
return false
}
}
return self
}
}
Examples
Now given you array
let words = ["a", "a", "b", "c", "c", "c", "d", "d"]
You can produce a new array bringing the occurrences of "a" to different values
words.updated(numOccurrencies: 0, ofWord: "a")
// ["b", "c", "c", "c", "d", "d"]
words.updated(numOccurrencies: 1, ofWord: "a")
// ["a", "b", "c", "c", "c", "d", "d"]
words.updated(numOccurrencies: 2, ofWord: "a")
// ["a", "a", "b", "c", "c", "c", "d", "d"]
words.updated(numOccurrencies: 3, ofWord: "a")
// ["a", "a", "b", "c", "c", "c", "d", "d", "a"]
words.updated(numOccurrencies: 4, ofWord: "a")
// ["a", "a", "b", "c", "c", "c", "d", "d", "a", "a"]
Sorting
As you can see the new occurrences of "a" ad added at the end of the array. If you want the array to stay sorted just append .sorted() to each invocation
words.updated(numOccurrencies: 4, ofWord: "a").sorted()
// ["a", "a", "a", "a", "b", "c", "c", "c", "d", "d"]
"The maximum times I want a single string to be in the array is up to 10 times"
I am now assuming the output array must be sorted.
I am going to use a different approach for this. I will calculate for each word, the number of occurrences we expect for that word in the output array.
Each occurrences will be the minimum between 10 and the current occurrences for that word.
Example
a: min(10, 2) = 2
b: min(10, 1) = 1
...
Once I have the number of occurrences expected for each word I can build the final sorted array from scratch.
extension Array where Element == String {
func updated(withMaximumOccurrencies max: Int) -> [String] {
let countedSet = NSCountedSet(array: self)
let uniqueWords = Set(self)
return uniqueWords
.reduce([String]()) { (res, word) -> [String] in
let occurrencies = Swift.min(max, countedSet.count(for: word))
return res + [String](repeatElement(word, count: occurrencies))
}.sorted()
}
}
Examples
let words: [String] = ["a", "a", "b", "c", "c", "c", "d", "d"]
words.updated(withMaximumOccurrencies: 1)
["a", "b", "c", "d"]
words.updated(withMaximumOccurrencies: 2)
["a", "a", "b", "c", "c", "d", "d"]
words.updated(withMaximumOccurrencies: 10)
["a", "a", "b", "c", "c", "c", "d", "d"]