Sometimes we might need to filter a list of records. For instance : We have an array of employees and we want to get all employees who live in the city Dehradun.

Here is the structure of Employee class :

@interface Employee : NSObject

@property (nonatomic,strong) NSString *name;
@property (nonatomic,strong) NSString *city;
@property (nonatomic,assign) float salary;

@end 

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city=%@",@"Dehradun"];
    NSArray *filteredArray = [empArr filteredArrayUsingPredicate:predicate];

For a case insensitive filter we can use [c] like this :

 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city=[c]%@",@"dehradun"]; 

We can also combine conditions. Like if we want to get employees with name 'John' or city 'Dehradun' we can do :

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(city=%@)||(name=%@)",@"Dehradun",@"John"];

For AND condition we need to use &&

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(city=%@)&&(name=%@)",@"Dehradun",@"John"];

The left hand key path can also be substituted using %K.

 NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K=[c]%@",@"city",@"dehradun"]; 

Basic comparision operators =, == (equal) >=,=> (greaterthanorequal) <=, =< (lessthanorequal) > (greaterthan) < (lessthan) !=, <> (notequal)

BETWEEN operator Used for values lying within a range

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"salary BETWEEN %@",@[@1200,@20000]]; 

String Comparisons BEGINSWITH, CONTAINS, ENDSWITH, LIKE, MATCHES

With LIKE operator we can use * for unknown number of characters and ? for a single unknown character.

Following predicate will get all employees with city name ending with 'dun'

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city LIKE %@",@"*dun"];

Following predicate will get all employees with city name begining with 'Dehra' and having 3 more characters in the end.

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"city LIKE %@",@"Dehra???"];

Predicates also work for array of nsdictionaries.

All of above mentioned and other comparisons can be seen in detail in Apple documentation here