NSSet和NSArry的区别&NSSet的一般用法

引用自：http://zhidao.baidu.com/link?url=uD25s5OdnfmnNzvEUcYl3eCuSNE20BytMTgTQ_L42YM3B0DWWCR3Fj3gBStI09GKBwJT1obbGSnPWgwDlr-7X1qByLjjn8VORAjMygfxJZ3

http://blog.csdn.net/ms2146/article/details/8657011

1.NSSet和NSArry的区别：

NSSet到底什么类型,其实它和NSArray功能性质一样,用于存储对象,属于集合； NSSet , NSMutableSet类声明编程接口对象,无序的集合,在内存中存储方式是不连续的,不像NSArray,NSDictionary（都是有序的集合）类声明编程接口对象是有序集合,在内存中存储位置是连续的；
NSSet和我们常用NSArry区别是：在搜索一个一个元素时NSSet比NSArray效率高,主要是它用到了一个算法hash(散列,也可直译为哈希)；开发文档中这样解释：You can use sets as an alternative to arrays when the order of elements isn’t important and performance in testing whether an object is contained in the set is a consideration—while arrays are ordered, testing for membership is slower than with sets.
比如你要存储元素A,一个hash算法直接就能直接找到A应该存储的位置；同样,当你要访问A时,一个hash过程就能找到A存储的位置.而对于NSArray,若想知道A到底在不在数组中,则需要便利整个数组,显然效率较低了；
NSSet,NSArray都是类,只能添加cocoa对象,如果需要加入基本数据类型（int,float,BOOL,double等）,需要将数据封装成NSNumber类型.

2.NSSet的一般用法

  
  
  
  
#import <Foundation/Foundation.h>


int main(int argc, const char * argv[])
{

    @autoreleasepool {

        NSSet *set1 = [NSSet setWithObjects:@"a", @"b", @"c", @"d", nil];
        NSSet *set2 = [[NSSet alloc] initWithObjects:@"1", @"2", @"3", nil];
        NSArray *array = [NSArray arrayWithObjects:@"a", @"b", @"c", nil];
        NSSet *set3 = [NSSet setWithArray:array];

        NSLog(@"set1 :%@", set1);
        NSLog(@"set2 :%@", set2);
        NSLog(@"set3 :%@", set3);

        //获取集合个数
        NSLog(@"set1 count :%d", set1.count);

        //以数组的形式获取集合中的所有对象
        NSArray *allObj = [set2 allObjects];
        NSLog(@"allObj :%@", allObj);

        //获取任意一对象
        NSLog(@"anyObj :%@", [set3 anyObject]);

        //是否包含某个对象
        NSLog(@"contains :%d", [set3 containsObject:@"obj2"]);


        //是否包含指定set中的对象
        NSLog(@"intersect obj :%d", [set1 intersectsSet:set3]);

        //是否完全匹配
        NSLog(@"isEqual :%d", [set2 isEqualToSet:set3]);

        //是否是子集合
        NSLog(@"isSubSet :%d", [set3 isSubsetOfSet:set1]);



        NSSet *set4 = [NSSet setWithObjects:@"a", @"b", nil];
        NSArray *ary = [NSArray arrayWithObjects:@"1", @"2", @"3", @"4", nil];
        NSSet *set5 = [set4 setByAddingObjectsFromArray:ary];
        NSLog(@"addFromArray :%@", set5);




        NSMutableSet *mutableSet1 = [NSMutableSet setWithObjects:@"1", @"2", @"3", nil];
        NSMutableSet *mutableSet2 = [NSMutableSet setWithObjects:@"a", @"2", @"b", nil];
        NSMutableSet *mutableSet3 = [NSMutableSet setWithObjects:@"1", @"c", @"b", nil];

        //集合元素相减
        [mutableSet1 minusSet:mutableSet2];
        NSLog(@"minus :%@", mutableSet1);

        //只留下相等元素
        [mutableSet1 intersectSet:mutableSet3];
        NSLog(@"intersect :%@", mutableSet1);

        //合并集合
        [mutableSet2 unionSet:mutableSet3];
        NSLog(@"union :%@", mutableSet2);

        //删除指定元素
        [mutableSet2 removeObject:@"a"];
        NSLog(@"removeObj :%@", mutableSet2);


        //删除所有数据
        [mutableSet2 removeAllObjects];
        NSLog(@"removeAll :%@", mutableSet2);

    }
    return 0;
}
 
日志:

  
  
  
  
 set1 :{(
    d,
    b,
    c,
    a
)}
 set2 :{(
    1,
    2,
    3
)}
 set3 :{(
    a,
    b,
    c
)}
 set1 count :4
 allObj :(
    1,
    2,
    3
)
 anyObj :a
 contains :0
 intersect obj :1
 isEqual :0
 isSubSet :1
 addFromArray :{(
    3,
    b,
    1,
    4,
    2,
    a
)}
 minus :{(
    1,
    3
)}
 intersect :{(
    1
)}
 union :{(
    b,
    1,
    2,
    a,
    c
)}
 removeObj :{(
    b,
    1,
    2,
    c
)}
 removeAll :{(
)}