iPhone - 从NSArray对象获取唯一值 [英] iPhone - getting unique values from NSArray object

问题描述

我有一个由自定义类的对象组成的 NSArray 。该类有3个（city，state，zip）字符串属性。我想从数组中获取所有唯一的状态值。

I have an NSArray formed with objects of a custom class. The class has 3 (city, state, zip) string properties. I would like to get all unique state values from the array.

我读过 NSPredicate 类但在这种情况下无法充分利用它。我能找到的唯一例子是字符串操作。

I did read through the NSPredicate class but couldn't make much of how to use it in this case. The only examples I could find were for string operations.

有人可以帮帮我吗？

推荐答案

完全简单的一个班轮：

NSSet *uniqueStates = [NSSet setWithArray:[myArrayOfCustomObjects valueForKey:@"state"]];

诀窍是 valueForKey：方法的NSArray 。这将遍历您的数组（ myArrayOfCustomObjects ），在每个对象上调用 -state 方法，并构建一个数组结果。然后我们使用生成的状态数组创建一个 NSSet 来删除重复项。

The trick is the valueForKey: method of NSArray. That will iterate through your array (myArrayOfCustomObjects), call the -state method on each object, and build an array of the results. We then create an NSSet with the resulting array of states to remove duplicates.

从iOS 5和OS X 10.7开始，还有一个新类可以执行此操作： NSOrderedSet 。有序集的优点是它将删除任何重复项，但也保持相对顺序。

Starting with iOS 5 and OS X 10.7, there's a new class that can do this as well: NSOrderedSet. The advantage of an ordered set is that it will remove any duplicates, but also maintain relative order.

NSArray *states = [myArrayOfCustomObjects valueForKey:@"state"];
NSOrderedSet *orderedSet = [NSOrderedSet orderedSetWithArray:states];
NSSet *uniqueStates = [orderedSet set];

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