Orginally this was used for a project I worked on where the user was creating a sort of journal entry that had a title. You'd pass the title into this parser and when the user wanted to add a cover photo to the entry using Unsplash, the parser would parse the entry title so when Unsplash appears, it already showed relevant results to the entry.

StringQueryParserUsingNSLinguisticsTagger.swift

// This was originally done in Playgrounds
// You can plop this in Playgrounds and it should work.

import UIKit

let title = "The best camping trip of the year with the best friends"

func checkForValidQueryString(_ string: String) -> Bool {
	guard
		!string.isEmpty,
		// When the user was creating an entry, they could create what was called a Moment or a Story.
		// We want to make sure the user has added an actual title before parsing, not using the placeholders.
		string != "Moment Name",
		string != "Story Name"
	else { return false }

	return true
}

func parseImportantWords(from string: String) -> String {
	var result = ""
	let options = NSLinguisticTagger.Options.omitWhitespace.rawValue | NSLinguisticTagger.Options.joinNames.rawValue
	let tagger = NSLinguisticTagger(tagSchemes: NSLinguisticTagger.availableTagSchemes(forLanguage: "en"), options: Int(options))

	tagger.string = string

	let range = NSRange(location: 0, length: string.utf16.count)
	tagger.enumerateTags(in: range,
						 scheme: .nameTypeOrLexicalClass,
						 options: NSLinguisticTagger.Options(rawValue: options)) { tag, tokenRange, sentenceRange, stop in
		guard let range = Range(tokenRange, in: string) else { return }
		let token = string[range]
		if let tag = tag {
			if tag.rawValue == "Noun" || tag.rawValue == "Verb" {
				guard !result.contains(token) else { return }
				result += "\(token) "
			}
		}
	}

	return result
}

/// Validates string from Moment or Story Title and produces a relevant starting query.
func produceQueryString(from input: String) -> String {
	let startingQuery: String

	if checkForValidQueryString(input) {
		startingQuery = parseImportantWords(from: input)
	} else {
		// If there is no valid string to parse, then I just gave it word that is general, but relevant to the app.
		startingQuery = "life"
	}

	return startingQuery
}

let startingQuery = produceQueryString(from: title)
print("Query: \(startingQuery)")