Predicates and sorting in iOS Swift

Introduction

Predicates help you find specific items in a list. Sorting arranges items in order, like alphabetically or by number.

You want to show only contacts whose names start with 'A'.

You need to list tasks sorted by their due date.

Filtering a list of products to show only those under $20.

Sorting messages by newest first.

Finding all photos taken in a certain year.

Syntax

iOS Swift

let predicate = NSPredicate(format: "propertyName CONTAINS[c] %@", "value")
let sortedArray = array.sorted { $0.property < $1.property }

NSPredicate uses a format string to describe the filter condition.

Sorting uses the sorted method with a closure to compare items.

Examples

This finds items where the name starts with 'J', ignoring case.

iOS Swift

let predicate = NSPredicate(format: "name BEGINSWITH[c] %@", "J")

This finds items where the age is 18 or older.

iOS Swift

let predicate = NSPredicate(format: "age >= %d", 18)

This sorts people by age from youngest to oldest.

iOS Swift

let sortedArray = people.sorted { $0.age < $1.age }

This sorts people by name alphabetically, ignoring case.

iOS Swift

let sortedArray = people.sorted { $0.name.localizedCaseInsensitiveCompare($1.name) == .orderedAscending }

Sample App

This program filters a list of people to only those whose names start with 'a' or 'A'. Then it sorts them by age from youngest to oldest. Finally, it prints their names and ages.

iOS Swift

import UIKit

class Person: NSObject {
  let name: String
  let age: Int
  init(name: String, age: Int) {
    self.name = name
    self.age = age
    super.init()
  }
}

let people = [
  Person(name: "Alice", age: 30),
  Person(name: "Bob", age: 20),
  Person(name: "Charlie", age: 25),
  Person(name: "anna", age: 22)
]

// Filter people whose name starts with 'A' or 'a'
let predicate = NSPredicate(format: "name BEGINSWITH[c] %@", "A")
let filteredPeople = people.filter { predicate.evaluate(with: $0) }

// Sort filtered people by age ascending
let sortedPeople = filteredPeople.sorted { $0.age < $1.age }

for person in sortedPeople {
  print("\(person.name) - \(person.age)")
}

Important Notes

NSPredicate is powerful for filtering arrays or Core Data fetch requests.

Sorting closures return true if the first item should come before the second.

Use [c] in predicates to ignore case when matching strings.

Summary

Predicates filter lists by conditions you set.

Sorting arranges items in order using a comparison.

Combine filtering and sorting to show exactly what you want in the right order.