sortedArrayUsingComparator 返回不正确的结果答案

【问题标题】：sortedArrayUsingComparator returning incorrect resultssortedArrayUsingComparator 返回不正确的结果
【发布时间】：2014-06-22 06:02:38
【问题描述】：

我有一个数组，其中包含一组时间戳（作为字符串），并且它们按排序顺序排列。我只想再次对它们进行排序，看看是否返回了相同的列表（原因是我将处理乱序存储的进一步时间戳，并且需要对它们进行排序）。这是我的日期数组，其中时间戳基本上是字符串：

(
"Jun 18, 2014 12:00:00 AM",
"Jun 18, 2014 12:15:00 AM",
"Jun 18, 2014 12:30:00 AM",
"Jun 18, 2014 12:45:00 AM",
"Jun 18, 2014 1:00:00 AM",
"Jun 18, 2014 1:15:00 AM",
"Jun 18, 2014 1:30:00 AM",
"Jun 18, 2014 1:45:00 AM",
"Jun 18, 2014 2:00:00 AM",
"Jun 18, 2014 2:15:00 AM",
"Jun 18, 2014 2:30:00 AM",
"Jun 18, 2014 2:45:00 AM",
"Jun 18, 2014 3:00:00 AM",
"Jun 18, 2014 3:15:00 AM",
"Jun 18, 2014 3:30:00 AM",
"Jun 18, 2014 4:15:00 AM",
"Jun 18, 2014 4:30:00 AM",
"Jun 18, 2014 4:45:00 AM",
"Jun 18, 2014 5:15:00 AM",
"Jun 18, 2014 5:30:00 AM",
"Jun 18, 2014 5:45:00 AM",
"Jun 18, 2014 6:00:00 AM",
"Jun 18, 2014 6:15:00 AM",
"Jun 18, 2014 6:30:00 AM",
"Jun 18, 2014 6:45:00 AM",
"Jun 18, 2014 7:00:00 AM",
"Jun 18, 2014 7:15:00 AM",
"Jun 18, 2014 7:30:00 AM",
"Jun 18, 2014 7:45:00 AM",
"Jun 18, 2014 8:00:00 AM",
"Jun 18, 2014 8:15:00 AM",
"Jun 18, 2014 8:30:00 AM",
"Jun 18, 2014 8:45:00 AM",
"Jun 18, 2014 9:00:00 AM",
"Jun 18, 2014 9:15:00 AM",
"Jun 18, 2014 10:00:00 AM",
"Jun 18, 2014 10:15:00 AM",
"Jun 18, 2014 10:30:00 AM",
"Jun 18, 2014 10:45:00 AM",
"Jun 18, 2014 11:15:00 AM",
"Jun 18, 2014 11:30:00 AM",
"Jun 18, 2014 11:45:00 AM",
"Jun 18, 2014 12:00:00 PM",
"Jun 18, 2014 12:15:00 PM",
"Jun 18, 2014 12:30:00 PM",
"Jun 18, 2014 12:45:00 PM",
"Jun 18, 2014 1:00:00 PM",
"Jun 18, 2014 1:15:00 PM",
"Jun 18, 2014 1:30:00 PM",
"Jun 18, 2014 2:00:00 PM",
"Jun 18, 2014 2:15:00 PM",
"Jun 18, 2014 2:30:00 PM",
"Jun 18, 2014 2:45:00 PM",
"Jun 18, 2014 3:00:00 PM",
"Jun 18, 2014 3:15:00 PM",
"Jun 18, 2014 3:45:00 PM",
"Jun 18, 2014 4:00:00 PM",
"Jun 18, 2014 4:15:00 PM",
"Jun 18, 2014 4:45:00 PM",
"Jun 18, 2014 5:15:00 PM",
"Jun 18, 2014 5:30:00 PM",
"Jun 18, 2014 6:00:00 PM",
"Jun 18, 2014 6:15:00 PM",
"Jun 18, 2014 7:00:00 PM",
"Jun 18, 2014 7:15:00 PM",
"Jun 18, 2014 7:30:00 PM",
"Jun 18, 2014 8:00:00 PM",
"Jun 18, 2014 8:15:00 PM",
"Jun 18, 2014 8:30:00 PM",
"Jun 18, 2014 9:15:00 PM",
"Jun 18, 2014 9:30:00 PM",
"Jun 18, 2014 9:45:00 PM",
"Jun 18, 2014 10:15:00 PM",
"Jun 18, 2014 10:30:00 PM",
"Jun 18, 2014 11:15:00 PM",
"Jun 18, 2014 11:30:00 PM",
"Jun 18, 2014 11:45:00 PM"
)

上面的数组是排序的时间戳。现在，如果我按升序对它们重新排序，它们应该给我相同的结果，但我想得到的结果是乱序的。我只是不明白为什么我会看到这样的行为：这是我得到的输出：

sorted dates = (
"Jun 18, 2014 12:00:00 AM",
"Jun 18, 2014 1:00:00 AM",
"Jun 18, 2014 2:00:00 AM",
"Jun 18, 2014 3:00:00 AM",
"Jun 18, 2014 6:00:00 AM",
"Jun 18, 2014 7:00:00 AM",
"Jun 18, 2014 8:00:00 AM",
"Jun 18, 2014 9:00:00 AM",
"Jun 18, 2014 10:00:00 AM",
"Jun 18, 2014 12:15:00 AM",
"Jun 18, 2014 1:15:00 AM",
"Jun 18, 2014 2:15:00 AM",
"Jun 18, 2014 3:15:00 AM",
"Jun 18, 2014 4:15:00 AM",
"Jun 18, 2014 5:15:00 AM",
"Jun 18, 2014 6:15:00 AM",
"Jun 18, 2014 7:15:00 AM",
"Jun 18, 2014 8:15:00 AM",
"Jun 18, 2014 9:15:00 AM",
"Jun 18, 2014 10:15:00 AM",
"Jun 18, 2014 11:15:00 AM",
"Jun 18, 2014 12:30:00 AM",
"Jun 18, 2014 1:30:00 AM",
"Jun 18, 2014 2:30:00 AM",
"Jun 18, 2014 3:30:00 AM",
"Jun 18, 2014 4:30:00 AM",
"Jun 18, 2014 5:30:00 AM",
"Jun 18, 2014 6:30:00 AM",
"Jun 18, 2014 7:30:00 AM",
"Jun 18, 2014 8:30:00 AM",
"Jun 18, 2014 10:30:00 AM",
"Jun 18, 2014 11:30:00 AM",
"Jun 18, 2014 12:45:00 AM",
"Jun 18, 2014 1:45:00 AM",
"Jun 18, 2014 2:45:00 AM",
"Jun 18, 2014 4:45:00 AM",
"Jun 18, 2014 5:45:00 AM",
"Jun 18, 2014 6:45:00 AM",
"Jun 18, 2014 7:45:00 AM",
"Jun 18, 2014 8:45:00 AM",
"Jun 18, 2014 10:45:00 AM",
"Jun 18, 2014 11:45:00 AM",
"Jun 18, 2014 12:00:00 PM",
"Jun 18, 2014 1:00:00 PM",
"Jun 18, 2014 2:00:00 PM",
"Jun 18, 2014 3:00:00 PM",
"Jun 18, 2014 4:00:00 PM",
"Jun 18, 2014 6:00:00 PM",
"Jun 18, 2014 7:00:00 PM",
"Jun 18, 2014 8:00:00 PM",
"Jun 18, 2014 12:15:00 PM",
"Jun 18, 2014 1:15:00 PM",
"Jun 18, 2014 2:15:00 PM",
"Jun 18, 2014 3:15:00 PM",
"Jun 18, 2014 4:15:00 PM",
"Jun 18, 2014 5:15:00 PM",
"Jun 18, 2014 6:15:00 PM",
"Jun 18, 2014 7:15:00 PM",
"Jun 18, 2014 8:15:00 PM",
"Jun 18, 2014 9:15:00 PM",
"Jun 18, 2014 10:15:00 PM",
"Jun 18, 2014 11:15:00 PM",
"Jun 18, 2014 12:30:00 PM",
"Jun 18, 2014 1:30:00 PM",
"Jun 18, 2014 2:30:00 PM",
"Jun 18, 2014 5:30:00 PM",
"Jun 18, 2014 7:30:00 PM",
"Jun 18, 2014 8:30:00 PM",
"Jun 18, 2014 9:30:00 PM",
"Jun 18, 2014 10:30:00 PM",
"Jun 18, 2014 11:30:00 PM",
"Jun 18, 2014 12:45:00 PM",
"Jun 18, 2014 2:45:00 PM",
"Jun 18, 2014 3:45:00 PM",
"Jun 18, 2014 4:45:00 PM",
"Jun 18, 2014 9:45:00 PM",
"Jun 18, 2014 11:45:00 PM"
)

例如，为什么“2014 年 6 月 18 日上午 12:15:00”会显示在“2014 年 6 月 18 日上午 1:00:00”之后？我只是不明白这部分！

这是我的代码：

-(void)sortDates {
NSDateFormatter *dateFormatter;

dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"MMM dd, yyyy HH:mm:ss a"];

NSLog(@"%@", xAxisDataWithDate);
NSArray *sortedTimes = [xAxisDataWithDate sortedArrayUsingComparator:^NSComparisonResult(NSString *obj1, NSString *obj2)
{
    NSDate *date1 = [dateFormatter dateFromString:obj1];
    NSDate *date2 = [dateFormatter dateFromString:obj2];
    return [date1 compare:date2];
}];
NSLog(@"sorted dates = %@", sortedTimes);
}

我还编写了一个示例程序，其中包含这些日期的子集，当数组中存在 1:00:00 AM 时，它似乎给了我错误的结果（1:00:00 AM 应该在 12 之后存储： 00:00 AM）：

-(void)sortDates {
NSDateFormatter *dateFormatter;

dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"MMM dd, yyyy HH:mm:ss a"];

NSMutableArray *times = [[NSMutableArray alloc]initWithObjects:@"Jun 19, 2014 11:45:00 PM", @"Jun 18, 2014 1:00:00 AM", @"Jun 18, 2014 12:15:00 AM",@"Jun 18, 2014 12:00:00 AM", nil];
NSArray *sortedTimes = [times sortedArrayUsingComparator:^NSComparisonResult(NSString *obj1, NSString *obj2)
{
    NSDate *date1 = [dateFormatter dateFromString:obj1];
    NSDate *date2 = [dateFormatter dateFromString:obj2];
    return [date1 compare:date2];
}];
NSLog(@"sorted dates = %@", sortedTimes);
}

输出：

sorted dates = (
"Jun 18, 2014 1:00:00 AM",
"Jun 18, 2014 12:00:00 AM",
"Jun 18, 2014 12:15:00 AM",
"Jun 19, 2014 11:45:00 PM"
)

我无法弄清楚为什么我的结果与 NSMutableArray *xAxisDataWithDate 和 w.r.t NSMutableArray *times 不一致！请在这方面帮助我！赞赏。

【问题讨论】：

你应该使用“hh”来表示小时，因为你在上午/下午使用 1-12。 “HH”代表 0-23。此外，请务必将日期格式的语言环境设置为某些标准语言环境（可能是[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"]），而不是让它选择系统语言环境，因为这会有所不同。综上所述，您可能应该使用日期对象而不是字符串开头。
另外，尝试记录您的格式化程序为两个字符串提供的NSDate 对象，这些字符串最终相对于彼此排序不正确。看看它是如何解释这些字符串的。
谢谢肯。这对我有用！非常感谢您的帮助。

标签： ios iphone objective-c nsdate nsdateformatter

【解决方案1】：

您的格式似乎错误，时间似乎是 12 小时格式，请将格式更改为 MMM dd, yyyy hh:mm:ss a note lowercase "h"

"Jun 18, 2014 12:00:00 AM",
"Jun 18, 2014 12:15:00 AM",
"Jun 18, 2014 1:00:00 AM",
"Jun 19, 2014 11:45:00 PM"

更重要的是，您应该在比较之前将字符串转换为日期，sortedArray… 使用合并排序，因此您将字符串转换为日期n log n 次而不是n 次

【讨论】：