Importing from second array in Swift - arrays

Question

I have 2 arrays, 1 is a master (bookArray) and the other an update list (stockBooksArray). I use the loop below to import new data into waster array using a unique record (isbn) that exists in both arrays.
Is there a way to improve the performance of the loop below?
The update array can contain a different count to the master, sometimes more, sometimes less.
for i in 0...stockBooksArray.count {
let StockFiltered = stockBooksArray.filter{$0.isbn == bookArray[i].isbn}
if StockFiltered.count != 0 {
bookArray[i].stockAmount = StockFiltered[0].Stock
bookArray[i].unitCost = StockFiltered[0].Cost
bookArray[i].dues = StockFiltered[0].dues
bookArray[i].stockRRP = StockFiltered[0].RRP
}
}
Thanks,
Anthony

Answer 1

Yes there is. Right now you are looping through the bookArray array once for every stockBooksArray object. That's O(N*M) which is pretty bad.
Instead, if you can sort both arrays by ISBN, then you can step through both at the same time, visiting each element only once which would be O(N). Considerably faster, even if you include the time to sort them.
I threw the code below together pretty quick. It assumes that both arrays are sorted by isbn. I think you will find this considerably faster.
var j = 0
for book in stockBooksArray {
while bookArray[j].isbn < book.isbn && j < bookArray.count {
++j;
}
if j == bookArray.count {
break
}
else if bookArray[j].isbn == book.isbn {
bookArray[j].stockAmount = StockFiltered[0].Stock
bookArray[j].unitCost = StockFiltered[0].Cost
bookArray[j].dues = StockFiltered[0].dues
bookArray[j].stockRRP = StockFiltered[0].RRP
}
}

Answer 2

If you are just adding new ones you could get an NSMutableSet of the ISBNs for each, perform a set minusSet: operation removing the bookArray ISBNs from stockBooksArray and then just add the resulting ISBNs to bookArray.
Untested concept code, convert to Swift as needed:
NSMutableSet *stockBooksSet = NSMutableSet setWithArray:[stockBooksSet valueForKey:#"isbn"];
NSSet *booksSet = NSSet setWithArray:[bookArray valueForKey:#"isbn"];
[stockBooksSet minusSet: booksSet];
for (NSString *isbn in stockBooksSet) {
// add book with ism to booksSet
}

Answer 3

Updated code using Daniel T. method.
bookArray.sort { (lhs, rhs) in return lhs.isbn < rhs.isbn }
stockBooksArray.sort { (lhs, rhs) in return lhs.isbn < rhs.isbn }
var j = 0
for book in stockBooksArray {
while bookArray[j].isbn < book.isbn && j < bookArray.count {
++j
}
if j == bookArray.count {
break
}
else if bookArray[j].isbn == book.isbn {
bookArray[j].stockAmount = book.Stock
bookArray[j].unitCost = book.Cost
bookArray[j].dues = book.dues
bookArray[j].stockRRP = book.RRP
}
}
From 5-6 seconds on iPad2 to almost instant.
Many thanks,
Anthony