Objective-C Programming: The Big Nerd Ranch Guide

Filtering

When you filter a collection, you compare its objects to a logical statement to get a resultant collection that only contains objects for which the statement is true.

A predicate contains a statement that might be true, like “The employeeID is greater than 75.” There is a class called NSPredicate. NSMutableArray has a handy method for discarding all the objects that do not satisfy the predicate:

-​ ​(​v​o​i​d​)​f​i​l​t​e​r​U​s​i​n​g​P​r​e​d​i​c​a​t​e​:​(​N​S​P​r​e​d​i​c​a​t​e​ ​*​)​p​r​e​d​i​c​a​t​e​;​

With NSArray, you cannot remove objects that do not match the predicate. Instead, NSArray has a method that creates a new array that contains all the objects that satisfy the predicate:

-​ ​(​N​S​A​r​r​a​y​ ​*​)​ ...