NSArray

##排序

• 逆序，array.reverseObjectEnumerator.allObjects
• 数组中是字符串对象排序首选sortedArrayUsingSelector:

NSArray *array = @[@"John Appleseed", @"Tim Cook", @"Hair Force One", @"Michael Jurewitz"];
NSArray *sortedArray = [array sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];

• 存储内容是数字

NSArray *numbers = @[@9, @5, @11, @3, @1];
NSArray *sortedNumbers = [numbers sortedArrayUsingSelector:@selector(compare:)];

• 使用函数指针sortedArrayHint排序

- (NSData *)sortedArrayHint;
- (NSArray *)sortedArrayUsingFunction:(NSInteger (*)(id, id, void *))comparator
     context:(void *)context;
- (NSArray *)sortedArrayUsingFunction:(NSInteger (*)(id, id, void *))comparator
     context:(void *)context hint:(NSData *)hint;

• 基于block的排序方法

- (NSArray *)sortedArrayUsingComparator:(NSComparator)cmptr;
- (NSArray *)sortedArrayWithOptions:(NSSortOptions)opts
     usingComparator:(NSComparator)cmptr;

• 性能比较selector最快

Sorting 1000000 elements. selector: 4947.90[ms] function: 5618.93[ms] block: 5082.98[ms].

• 更快的二分查找

typedef NS_OPTIONS(NSUInteger, NSBinarySearchingOptions) {
     NSBinarySearchingFirstEqual = (1UL << 8),
     NSBinarySearchingLastEqual = (1UL << 9),
     NSBinarySearchingInsertionIndex = (1UL << 10),
};

- (NSUInteger)indexOfObject:(id)obj
     inSortedRange:(NSRange)r
     options:(NSBinarySearchingOptions)opts
     usingComparator:(NSComparator)cmp;

//Time to search for 1000 entries within 1000000 objects. Linear: 54130.38[ms]. Binary: 7.62[ms]

枚举

• 使用indexesOfObjectsWithOptions:passingTest:

NSIndexSet *indexes = [randomArray indexesOfObjectsWithOptions:NSEnumerationConcurrent
     passingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
     return testObj(obj);
}];
NSArray *filteredArray = [randomArray objectsAtIndexes:indexes];

• 传统的枚举

NSMutableArray *mutableArray = [NSMutableArray array];
for (id obj in randomArray) {
     if (testObj(obj)) {
          [mutableArray addObject:obj];
     }
}

• block方式枚举

NSMutableArray *mutableArray = [NSMutableArray array];
[randomArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
     if (testObj(obj)) {
          [mutableArray addObject:obj];
     }
}];

• 通过下标objectAtIndex:

NSMutableArray *mutableArray = [NSMutableArray array];
for (NSUInteger idx = 0; idx < randomArray.count; idx++) {
     id obj = randomArray[idx];
     if (testObj(obj)) {
          [mutableArray addObject:obj];
     }
}

• 使用比较传统的学院派NSEnumerator

NSMutableArray *mutableArray = [NSMutableArray array];
NSEnumerator *enumerator = [randomArray objectEnumerator];
id obj = nil;
while ((obj = [enumerator nextObject]) != nil) {
     if (testObj(obj)) {
          [mutableArray addObject:obj];
     }
}

• 使用predicate

NSArray *filteredArray2 = [randomArray filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id obj, NSDictionary *bindings) {
     return testObj(obj);
}]];

• 各个方法枚举时间参考，indexesOfObjectsWithOptions在开启了并发枚举的情况下比NSFastEnumeration快一倍。

枚举方法 / 时间 [ms]	10.000.000 elements	10.000 elements
indexesOfObjects:, concurrent	1844.73	2.25
NSFastEnumeration (for in)	3223.45	3.21
indexesOfObjects:	4221.23	3.36
enumerateObjectsUsingBlock:	5459.43	5.43
objectAtIndex:	5282.67	5.53
NSEnumerator	5566.92	5.75
filteredArrayUsingPredicate:	6466.95	6.31

NSDictionary

性能

同样数目的值，NSDictionary比NSArray要花费多得多的内存空间

排序

使用NSArray的排序方法将键数组排序为新的对象

- (NSArray *)keysSortedByValueUsingSelector:(SEL)comparator;
- (NSArray *)keysSortedByValueUsingComparator:(NSComparator)cmptr;
- (NSArray *)keysSortedByValueWithOptions:(NSSortOptions)opts
     usingComparator:(NSComparator)cmptr;

枚举

• keysOfEntriesWithOptions:passingTest:，可并行

NSSet *matchingKeys = [randomDict keysOfEntriesWithOptions:NSEnumerationConcurrent
passingTest:^BOOL(id key, id obj, BOOL *stop)
{
     return testObj(obj);
}];
NSArray *keys = matchingKeys.allObjects;
NSArray *values = [randomDict objectsForKeys:keys notFoundMarker:NSNull.null];
__unused NSDictionary *filteredDictionary = [NSDictionary dictionaryWithObjects:values
     forKeys:keys];

• getObjects:andKeys: 枚举，基于c数组

NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionary];
id __unsafe_unretained objects[numberOfEntries];
id __unsafe_unretained keys[numberOfEntries];
[randomDict getObjects:objects andKeys:keys];
for (int i = 0; i < numberOfEntries; i++) {
     id obj = objects[i];
     id key = keys[i];
     if (testObj(obj)) {
          mutableDictionary[key] = obj;
     }
}

• block枚举

NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionary];
[randomDict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
     if (testObj(obj)) {
          mutableDictionary[key] = obj;
     }
}];

• NSFastEnumeration

NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionary];
for (id key in randomDict) {
     id obj = randomDict[key];
     if (testObj(obj)) {
          mutableDictionary[key] = obj;
     }
}

• NSEnumeration

NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionary];
NSEnumerator *enumerator = [randomDict keyEnumerator];
id key = nil;
while ((key = [enumerator nextObject]) != nil) {
     id obj = randomDict[key];
     if (testObj(obj)) {
          mutableDictionary[key] = obj;
     }
}

• 各个方法枚举时间参考

枚举方法 / 时间 [ms]	50.000 elements	1.000.000 elements
keysOfEntriesWithOptions:, concurrent	16.65	425.24
getObjects:andKeys:	30.33	798.49
keysOfEntriesWithOptions:	30.59	856.93
enumerateKeysAndObjectsUsingBlock:	36.33	882.93
NSFastEnumeration	41.20	1043.42
NSEnumeration	42.21	1113.08