objective-c 中数据类型之三 数组（NSArray） 高级操作

1. 求数组中元素的和

NSArray *array = @[ @1, @2, @3, @4, @5, @3 ];NSNumber *sum = [array valueForKeyPath:@"@sum.integerValue"];NSLog(@"sum = %@", sum);    // sum = 18

2. 求数组中元素的平均值

NSNumber *avg = [array valueForKeyPath: @"@avg.integerValue"];NSLog(@"avg = %@", avg);    // avg = 3

3. 求数组中元素的最大值

NSNumber *max = [array valueForKeyPath: @"@max.integerValue"];NSLog(@"max = %@", max);    // max = 5

4. 求数组中元素的最小值

NSNumber *min = [array valueForKeyPath: @"@min.integerValue"];NSLog(@"min = %@", min);    // min = 1

5. 返回数组中不重复的数据

NSArray *distinctArray = [array valueForKeyPath:@"@distinctUnionOfObjects.integerValue"];NSLog(@"distinctArray = %@", distinctArray);    // distinctArray = ( 3, 2, 5, 1, 4 )

6. 返回数组中大于3的元素（小于 等于 类似）

NSPredicate *pre = [NSPredicate predicateWithFormat:@"self > 3"];NSArray *preArray = [array filteredArrayUsingPredicate:pre];NSLog(@"preArray = %@", preArray);    // preArray = ( 4, 5 )

7. 从小到大排序

NSArray *sortedArray = [array sortedArrayUsingSelector:@selector(compare:)];NSLog(@"sortedArray = %@", sortedArray);    // sortedArray = ( 1, 2, 3, 3, 4, 5 )

8. 从大到小排序

NSComparator cmptr  = ^(id obj1, id obj2){        return (-1)*[obj1 compare:obj2];    };NSArray *revertsortedArray = [array sortedArrayWithOptions:NSSortStable usingComparator:cmptr];NSLog(@"revertsortedArray = %@", revertsortedArray);    // revertsortedArray = ( 5, 4, 3, 3, 2, 1 )

9. 倒序排列

NSArray *revertArray = [[array reverseObjectEnumerator] allObjects];NSLog(@"revertArray = %@", revertArray);    // revertArray = ( 3, 5, 4, 3, 2, 1 )