如何实现“按值分组”在 NSMutableArray 中？

Question

我正在使用 NSMutableArray。我想按日期获取值，就像我们在 SQL group by "log_date" 中所做的那样。

logMuArray (
        {
        "log_currenttime" = "4:30pm";
        "log_date" = "11.12.2011";
        "log_duration" = "1:30";
    },
        {
        "log_currenttime" = "4:33pm";
        "log_date" = "11.12.2011";
        "log_duration" = "2:21";
    },
        {
        "log_currenttime" = "4:40pm";
        "log_date" = "11.12.2011";
        "log_duration" = "5:30";
    },
        {
        "log_currenttime" = "7:30pm";
        "log_date" = "12.12.2011";
        "log_duration" = "1:30";
    },
        {
        "log_currenttime" = "7:33pm";
        "log_date" = "12.12.2011";
        "log_duration" = "2:21";
    },
        {
        "log_currenttime" = "7:40pm";
        "log_date" = "12.12.2011";
        "log_duration" = "5:30";
    },
        {
        "log_currenttime" = "07:16pm";
        "log_date" = "19.12.2011";
        "log_duration" = "0:07";
    },
        {
        "log_currenttime" = "7:31pm";
        "log_date" = "19.12.2011";
        "log_duration" = "0:04";
    },
        {
        "log_currenttime" = "7:33pm";
        "log_date" = "19.12.2011";
        "log_duration" = "0:03";
    },
        {
        "log_currenttime" = "7:33pm";
        "log_date" = "19.12.2011";
        "log_duration" = "0:06";
    },
        {
        "log_currenttime" = "7:35pm";
        "log_date" = "19.12.2011";
        "log_duration" = "0:05";
    }
)

**所以，我刚刚执行了......

 NSLog(@"logMuArray %@",[logMuArray valueForKey:@"log_date"]);

但我只想获取唯一的日期。** 我考虑过 NSPredicate 或 Mutable Set 等...

logMuArray (
    "11.12.2011",
    "11.12.2011",
    "11.12.2011",
    "12.12.2011",
    "12.12.2011",
    "12.12.2011",
    "19.12.2011",
    "19.12.2011",
    "19.12.2011",
    "19.12.2011",
    "19.12.2011"
)

提前致谢...

编辑：

我也听说过“@distinctUnionOfObjects”

......

Answer 1

香蒂的答案很接近。您想要使用键值编码集合运算符 @distinctUnionOfObjects。将运算符放置在您希望其影响的键之前，就像它是您正在访问的键路径的一部分一样：

[logMuArray valueForKeyPath:@"@distinctUnionOfObjects.log_date"]

注意 valueForKeyPath:，而不是valueForKey: 前者是Key-Value中的方法编码协议，并允许访问任意深度的属性。键路径是由点分隔键组成的 NSString。每个密钥查找的结果依次用于访问下一个密钥（从原始接收者开始）；默认情况下，valueForKey: 在每一步都会被简单地调用。

Answer 2

您应该将 NSSet 用于独特的项目，例如：

NSSet *filteredData = [NSSet setWithArray:[logMuArray valueForKey:@"log_date"]];

Answer 3

您可以使用 KVC 为此。

[logMuArray valueForKey:@"@distinctUnionOfArrays.log_date"]

编辑：编辑乔希的回应

[logMuArray valueForKeyPath:@"@distinctUnionOfArrays.log_date"]

Answer 4

尝试这个逻辑可能对你有帮助

-(NSMutableArray *) makeUnique :(NSMutableArray *) array {    
    int i;
    int count = [array count];
    for (i =0; i< count ; i++) {
        NSRange range = NSMakeRange (i+1, count); 
        [array removeObject:[array objectAtIndex:i] inRange:range];
    }
    return array;
}

Answer 5

您可以合并一组

这里是一些示例代码

NSMutableArray * mArray = [NSMutableArray array];
NSDictionary *d1 = [NSDictionary dictionaryWithObjectsAndKeys:@"foo",@"bar",@"bar",@"oooo",nil];
NSDictionary *d2 = [NSDictionary dictionaryWithObjectsAndKeys:@"boo",@"bar",@"bar",@"oooo",nil];
NSDictionary *d3 = [NSDictionary dictionaryWithObjectsAndKeys:@"boo",@"bar",@"bar",@"oooo",nil];
[mArray addObject:d1];
[mArray addObject:d2];
[mArray addObject:d3];
NSLog(@"the array\n%@", mArray);
NSLog(@"just bar %@", [mArray valueForKey:@"bar"]);
//get unique values
NSSet * set = [NSSet setWithArray:[mArray valueForKey:@"bar"]];
NSLog(@"unique just bar %@", [set allObjects]);

，这里是输出

2011-12-20 01:50:59.034 TestEnvironment[32401:207] the array
(
        {
        bar = foo;
        oooo = bar;
    },
        {
        bar = boo;
        oooo = bar;
    },
        {
        bar = boo;
        oooo = bar;
    }
)
2011-12-20 01:50:59.036 TestEnvironment[32401:207] just bar (
    foo,
    boo,
    boo
)
2011-12-20 01:50:59.038 TestEnvironment[32401:207] unique just bar (
    foo,
    boo
)