using KVC on collection objects like NSArray and NSDictionary.

kvcDemo.md

KVCを使えば、このようなコードが自動的に値を計算してくれる。

KVC with special keyPath is really powerful for collection objects like NSArray and NSDictionary and NSSet

AppleのDocを見る

@max, @min, @sum, @avg

Sample 1 : One of the element in the array does not contain height property

  NSArray *testDicts = @[ @{ @"height" : @12 }, @{ @"height" : @13 }, @{ @"height" : @13 }, @{ @"height" : @13 }, @{ @"height" : @14 }, @{ @"height" : @15 }, @{ @"height" : @16 }, @{ @"id" : @17 } ];
  NSNumber *sum = [testDicts valueForKeyPath:@"@sum.height"];
  NSNumber *max = [testDicts valueForKeyPath:@"@max.height"];
  NSNumber *min = [testDicts valueForKeyPath:@"@min.height"];
  NSNumber *avg = [testDicts valueForKeyPath:@"@avg.height"];
  NSNumber *count = [testDicts valueForKeyPath:@"@count.height"];
  NSArray *distinctUnionOfObjects = [testDicts valueForKeyPath:@"@distinctUnionOfObjects.height"];
  NSArray *unionOfObjects = [testDicts valueForKeyPath:@"@unionOfObjects.height"];
  NSLog(@"sum = %@ | max = %@ | min = %@ | avg = %@ | count = %@", sum, max, min, avg, count);
  NSLog(@"\ndis: %@\nunion:%@", distinctUnionOfObjects, unionOfObjects);

2012-08-24 17:53:03.788 [GGTV] sum = 96 | max = 16 | min = 12 | avg = 12 | count = 8
2012-08-24 17:53:03.788 [GGTV] 
dis: (
    15,
    13,
    16,
    14,
    12
)
union:(
    12,
    13,
    13,
    13,
    14,
    15,
    16
)

Sample 2 : All the elements in Array contain property height

  NSArray *testDicts = @[ @{ @"height" : @12 }, @{ @"height" : @13 }, @{ @"height" : @13 }, @{ @"height" : @13 }, @{ @"height" : @14 }, @{ @"height" : @15 }, @{ @"height" : @16 }, @{ @"height" : @17 } ];
  NSNumber *sum = [testDicts valueForKeyPath:@"@sum.height"];
  NSNumber *max = [testDicts valueForKeyPath:@"@max.height"];
  NSNumber *min = [testDicts valueForKeyPath:@"@min.height"];
  NSNumber *avg = [testDicts valueForKeyPath:@"@avg.height"];
  NSNumber *count = [testDicts valueForKeyPath:@"@count.height"];
  NSArray *distinctUnionOfObjects = [testDicts valueForKeyPath:@"@distinctUnionOfObjects.height"];
  NSArray *unionOfObjects = [testDicts valueForKeyPath:@"@unionOfObjects.height"];
  NSLog(@"sum = %@ | max = %@ | min = %@ | avg = %@ | count = %@", sum, max, min, avg, count);
  NSLog(@"\ndis: %@\nunion:%@", distinctUnionOfObjects, unionOfObjects);

2012-08-24 17:54:35.986 [GGTV] sum = 113 | max = 17 | min = 12 | avg = 14.125 | count = 8
2012-08-24 17:54:35.986 [GGTV] 
dis: (
    17,
    15,
    13,
    16,
    14,
    12
)
union:(
    12,
    13,
    13,
    13,
    14,
    15,
    16,
    17
)

Conclusion

1. Sample 1 might be a bug, but we need to live with it now.
2. It's really convenient.