ios - 根据键的值从字典的 NSArray 中获取公共(public)元素

Question

我有 NSDictionaries 的 NSMutableArray。这是数组。

Month records (
    {
    BMI = "209.75";
    Date = "15/07/2014 09:03 AM";
    Height = 42;
    Weight = 37;
    day = 15;
    month = 7;
    year = 2014;
},
    {
    BMI = "366.67";
    Date = "21/07/2014 09:03 AM";
    Height = 30;
    Weight = 33;
    day = 21;
    month = 7;
    year = 2014;
},
    {
    BMI = "831.02";
    Date = "15/07/2014 09:04 AM";
    Height = 19;
    Weight = 30;
    day = 15;
    month = 7;
    year = 2014;
}
)  

现在我想获取相同“day”的元素(按照此处，“day=15”有 2 个元素，“day=7”有 1 个元素)。然后计算该特定日期的平均 BMI 值。

一般来说，我的要求是获取公共(public)元素(基于键的值)并将它们放入一个新数组中。在运行时使用大型数据集执行此操作的最佳方法是什么。

Answer 1

int day = /* ... */;
NSArray* recordsForDay = [records filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"day == %d", day]];

或:

NSIndexSet* indexes = [record indexesOfObjectsPassingTest:^BOOL (NSDictionar* record, NSUInteger idx, BOOL *stop) {
    return [[record objectForKey:@"day"] intValue] == day;
}];
NSArray* recordsForDay = [records objectsAtIndexes:indexes];