Question

我有一个很大的NSArray名字，我需要从该数组中随机获得4条记录（名称），我该怎么做？

Answer 1

#include <stdlib.h>

NSArray* names = ...;
NSMutableArray* pickedNames = [NSMutableArray new];

int remaining = 4;

if (names.count >= remaining) {
    while (remaining > 0) {
       id name = names[arc4random_uniform(names.count)];

       if (![pickedNames containsObject:name]) {
           [pickedNames addObject:name];
           remaining--;
       }
    }
}

Answer 2

我创建了一个名为NSArray+RandomSelection的类别。只需将此类别导入项目，然后使用

NSArray *things = ...
...
NSArray *randomThings = [things randomSelectionWithCount:4];

以下是实施：

NSArray+RandomSelection.h

@interface NSArray (RandomSelection)
    - (NSArray *)randomSelectionWithCount:(NSUInteger)count;
@end

NSArray+RandomSelection.m

@implementation NSArray (RandomSelection)

- (NSArray *)randomSelectionWithCount:(NSUInteger)count {
    if ([self count] < count) {
        return nil;
    } else if ([self count] == count) {
        return self;
    }

    NSMutableSet* selection = [[NSMutableSet alloc] init];

    while ([selection count] < count) {
        id randomObject = [self objectAtIndex: arc4random() % [self count]];
        [selection addObject:randomObject];
    }

    return [selection allObjects];
}

@end

Answer 3

如果您更喜欢 Swift框架，还有一些更方便的功能，请随时查看 HandySwift 。您可以将它添加到项目 via Carthage ，然后像这样使用它：

import HandySwift    

let names = ["Harry", "Hermione", "Ron", "Albus", "Severus"]
names.sample() // => "Hermione"

还可以选择一次多个随机元素：

names.sample(size: 3) // => ["Ron", "Albus", "Harry"]

我希望这有帮助！

从nsarray获取n个随机对象（例如4）

3 个答案: