#import "NSArray+Operation.h"
@implementation NSArray (Operation)
// 数组的平均数
-(float)averageValueOfElements{
NSNumber * value = [self valueForKeyPath:@"@avg.floatValue"];
return value.floatValue;
}
// 每个元素的和
-(float)sumValueOfElements{
NSNumber * value = [self valueForKeyPath:@"@sum.floatValue"];
return value.floatValue;
}
// 返回随机的子数组
-(NSArray *)randomizedArray{
if (self.count == 0) {
return self;
}
NSMutableArray *results = [NSMutableArray arrayWithArray:self];
NSUInteger i = [results count];
while(--i > 0) {
int j = arc4random() % (i+1);
[results exchangeObjectAtIndex:i withObjectAtIndex:j];
}
return [NSArray arrayWithArray:results];
}
//返回随机一个元素
- (id)hh_randomObject {
NSUInteger count = self.count;
return ((count > 0) ? self[arc4random_uniform((uint32_t)count)] : nil);
}
// 返回指定的某个
- (id)hh_objectOrNilAtIndex:(NSUInteger)index {
return index < self.count ? self[index] : nil;
}
原文：http://www.cnblogs.com/1018475062qq/p/7016617.html