objective-c - 使用 KVC 跨 n 个键查找最小值

Question

再次卡在 Obj-C 中的 KVC 上。

我想使用 KVC 来查找多个键中的最小值。

考虑以下数组:

NSArray *data = [[NSArray alloc] initWithObjects:
                 [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:2.0], @"a", [NSNumber numberWithFloat:5.0], @"b", [NSNumber numberWithFloat:4.0], @"c", nil],
                 [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:3.0], @"a", [NSNumber numberWithFloat:1.0], @"b", [NSNumber numberWithFloat:1.5], @"c", nil],
                 [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithFloat:9.0], @"a", [NSNumber numberWithFloat:7.0], @"b", [NSNumber numberWithFloat:6.0], @"c", nil],
                 nil];

我可以通过以下方式轻松找到“a”、“b”或“c”的最小值:

float minKeyA = [[data valueForKeyPath:@"@min.a"] floatValue];  // value: 2.0
float minKeyB = [[data valueForKeyPath:@"@min.b"] floatValue];  // value: 1.0
float minKeyC = [[data valueForKeyPath:@"@min.c"] floatValue];  // value: 1.5

我想要实现的是获取 NSSet 或 NSArray 的键，并找到这些键池中的最小值。

NSSet *keySet1 = [NSSet setWithObjects:@"a", @"b", nil]; 
// use to find absolute minimum value across keys 'a' and 'b' --> desired value 1.0
NSSet *keySet2 = [NSSet setWithObjects:@"a", @"c", nil];
// use to find absolute minimum value across keys 'a' and 'c' --> desired value 1.5
NSSet *keySet3 = [NSSet setWithObjects:@"a", @"b", @"c", nil];
// use to find absolute minimum value across keys 'a', 'b', and 'c' --> desired value 1.0

感谢任何指点:)

Answer 1

一个简单的解决方案是首先找到每个键的最小值，然后在第二步中找到这些最小值中的最小值。

NSMutableSet *localMinima = [NSMutableSet setWithCapacity:[keySet1 count]];
for (NSString *key in keySet1) {
    NSString *keyPath = [NSString stringWithFormat:@"@min.%@", key];
    NSNumber *localMin = [data valueForKeyPath:keyPath];
    [localMinima addObject:localMin];
}
NSNumber *globalMin = [localMinima valueForKeyPath:@"@min.self"];