Filter array with prefix - arrays

Question

I have an array, of type String:
var Arr = ["apple", "banana", "orange", "grapes", "yellow banana", "urban"]
How do I filter every word in array that has a prefix of my keyword?
Now I have this:
.filter { $0.contains(keyword) }
.sorted { ($0.hasPrefix(keyword) ? 0 : 1) < ($1.hasPrefix(keyword) ? 0 : 1) }
But if I have keyword "ban", it will return "banana", "yellow banana", and "urban".
I need only to filter prefix of every word in array element, to get "banana" and "yellow banana".

Answer 1

You can use a regular expression which checks if the keyword
occurs at a word boundary (\b pattern):
let array = ["apple", "banana", "orange", "grapes", "yellow banana", "urban"]
let keyword = "ban"
let pattern = "\\b" + NSRegularExpression.escapedPattern(for: keyword)
let filtered = array.filter {
$0.range(of: pattern, options: .regularExpression) != nil
}
print(filtered) // ["banana", "yellow banana"]
And for a case-insensitive search use
options: [.regularExpression, .caseInsensitive]
instead.

Answer 2

Performance Note
I just want to refer to the Time-Complexity caused by filtering the array for matching.
For example :
private var words: [String]
func words(matching prefix: String) -> [String]
{
return words.filter { $0.hasPrefix(prefix) }
}
words(matching:) will go through the collection of strings and return
the strings that match the prefix.
If the number of elements in the words array is small, this is a
reasonable strategy. But if you’re dealing with more than a few
thousand words, the time it takes to go through the words array will
be unacceptable. The time complexity of words(matching:) is O(k*n),
where k is the longest string in the collection, and n is the number of
words you need to check.
Trie data structure has excellent performance characteristics for
this type of problem.
Reference : https://www.raywenderlich.com/892-swift-algorithm-club-swift-trie-data-structure

Answer 3

You will need to first break up your string into words using enumerateSubstrings method and then you can check if any of the words contains the keyword prefix:
extension String {
var words: [String] {
var words: [String] = []
enumerateSubstrings(in: startIndex..<endIndex, options: .byWords) { word,_,_,_ in
guard let word = word else { return }
words.append(word)
}
return words
}
}
let arr = ["apple", "banana", "orange", "grapes", "yellow banana", "urban"]
let keyword = "ban"
let filtered = arr.filter { $0.words.contains(where: {$0.hasPrefix(keyword)}) }
filtered // ["banana", "yellow banana"]

Answer 4

Alternatively in Swift 3+:
let array = ["apple", "banana", "orange", "grapes", "yellow banana", "urban"]
let keyword = "ban"
let filtered = array.filter {
$0.components(separatedBy: " ").first { $0.hasPrefix(keyword) } != nil
}
print(filtered) // ["banana", "yellow banana"]

Answer 5

You can filter array with hasPrefix as follows:
// I Use two arrays, actualArray with original data and filteredArray contains data after filtration. You can use whatever is best for your scenario
filteredArray = actaulArray.filter({ $0.hasPrefix(searchBar.text!) })