Loop is taking too long to process - ios

Question

I am using following to code to arrange the array of contacts in sections (for e.g. contact with prefix "A" should show under "A" section). If there are contacts 4-5 hundred then it takes 20 sec to process.
Can you please check what is issue here? or any alternate for this.
let finalArr = NSMutableArray()
for contactDetail in conatctsArr {
let name = (contactDetail as! Dictionary)["givenName"] ?? ""// Getting First character of name
var key = String()
if name.characters.count > 0 {
let index1 = name.index((name.startIndex), offsetBy: 1)
key = name.substring(to: index1)
}
else {
key = ""
}
// getting all contatcts starting with particular character
let predicate=NSPredicate(format: "SELF.givenName beginswith[c] %#",key)
let filteredArr = (conatctsArr as NSArray).filtered(using: predicate)
var dic = Dictionary<String, Any>()
dic["key"] = key
dic["values"] = filteredArr
if filteredArr.count > 0 && !(finalArr.contains(dic)) {
finalArr.add(dic)
}
}

Answer 1

Removing the filtered elements from the array after processing in each loop might improve the performance. Try:
let finalArr = NSMutableArray()
var processingArray = NSMutableArray(array:conatctsArr)
while processingArray.count > 0 {
let contactDetail = processingArray[0]
let name = (contactDetail as! Dictionary)["givenName"] ?? ""
var key = String()
if name.characters.count > 0 {
let index1 = name.index((name.startIndex), offsetBy: 1)
key = name.substring(to: index1)
}
else {
key = ""
}
let predicate=NSPredicate(format: "SELF.givenName beginswith[c] %#",key)
let filteredArr = processingArray.filtered(using: predicate)
if filteredArr.count > 0 {
var dic = Dictionary<String, Any>()
dic["key"] = key
dic["values"] = filteredArr
finalArr.add(dic)
}
processingArray.removeObjects(in: filteredArr)
}

Answer 2

In your code, the filtering is being done multiple times for the same key. Try :
let finalArr = NSMutableArray()
for contactDetail in conatctsArr
{
let keysArray = [“A”, “B”, “C”,…. “Z”]
for key in keysArray
{
let predicate=NSPredicate(format: "SELF.givenName beginswith[c] %#",key)
let filteredArr = (conatctsArr as NSArray).filtered(using: predicate)
var dic = Dictionary<String, Any>()
dic["key"] = key
dic["values"] = filteredArr
if filteredArr.count > 0) {
finalArr.add(dic)
}
}
}