ios - indexOfObjectsPassingTest 或 filteredArrayUsingPredicate 哪个性能更快？

Question

当需要过滤 NSArray 以获取返回数组中项目的子集时，哪种方法更频繁且在边缘情况下更快？

Answer 1

以下测试(在 Release 模式下编译，在 Mac Pro 上执行)表明如果您使用 filteredArrayUsingPredicate 比 indexesOfObjectsPassingTest 慢一个“文本”谓词，但如果您使用基于 block 的谓词会更快。我测试中的 fasted 方法是一个简单的(快速枚举)循环，它添加了所有匹配项对象到可变数组。

过滤包含 10,000,000 个字典的数组的结果，其中约 50% 与谓词匹配:

8.514334 (predicateWithFormat)4.422550 (predicateWithBlock)5.170086 (indexesOfObjectsPassingTest)3.154015 (fast-enumeration + mutable array)

Of course the results may be different for other predicates.

#import <Foundation/Foundation.h>

NSUInteger filter1(NSArray *a)
{
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"num > 1000 AND foo == 'bar'"];
    NSArray *filtered = [a filteredArrayUsingPredicate:pred];
    return [filtered count];
}

NSUInteger filter2(NSArray *a)
{
    NSPredicate *pred = [NSPredicate predicateWithBlock:^BOOL(NSDictionary *obj, NSDictionary *bindings) {
        return ([obj[@"num"] intValue] > 1000 && [obj[@"foo"] isEqualToString:@"bar"]);
    }];
    NSArray *filtered = [a filteredArrayUsingPredicate:pred];
    return [filtered count];
}

NSUInteger filter3(NSArray *a)
{
    NSIndexSet *matching = [a indexesOfObjectsPassingTest:^BOOL(NSDictionary *obj, NSUInteger idx, BOOL *stop) {
        return ([obj[@"num"] intValue] > 1000 && [obj[@"foo"] isEqualToString:@"bar"]);
    }];
    NSArray *filtered = [a objectsAtIndexes:matching];
    return [filtered count];
}

NSUInteger filter4(NSArray *a)
{
    NSMutableArray *filtered = [NSMutableArray array];
    for (NSDictionary *obj in a) {
        if ([obj[@"num"] intValue] > 1000 && [obj[@"foo"] isEqualToString:@"bar"]) {
            [filtered addObject:obj];
        }
    }
    return [filtered count];
}

void testmethod(NSArray *a, NSUInteger(*method)(NSArray *a))
{
    @autoreleasepool {
        NSDate *t1 = [NSDate date];
        NSUInteger count = method(a);
        NSDate *t2 = [NSDate date];
        NSLog(@"%f", [t2 timeIntervalSinceDate:t1]);
    }
}

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        NSMutableArray *a = [NSMutableArray array];
        for (int i = 0; i < 10000000; i++) {
            [a addObject:@{@"num": @(arc4random_uniform(2000)), @"foo":@"bar"}];
        }
        testmethod(a, filter1);
        testmethod(a, filter2);
        testmethod(a, filter3);
        testmethod(a, filter4);
    }
    return 0;
}