NSArray等效地图

Question

给定一个NSArray的NSDictionary对象(含类似的对象和密钥)是有可能写出执行地图指定的键的阵列？例如,在Ruby中,它可以通过以下方式完成:

array.map(&:name)

Answer 1

它只保存了几行,但我在NSArray上使用了一个类别.您需要确保您的块永远不会返回nil,但除此之外,对于-[NSArray valueForKey:]无法工作的情况,它可以节省时间.

@interface NSArray (Map)

- (NSArray *)mapObjectsUsingBlock:(id (^)(id obj, NSUInteger idx))block;

@end

@implementation NSArray (Map)

- (NSArray *)mapObjectsUsingBlock:(id (^)(id obj, NSUInteger idx))block {
    NSMutableArray *result = [NSMutableArray arrayWithCapacity:[self count]];
    [self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
        [result addObject:block(obj, idx)];
    }];
    return result;
}

@end

用法很像-[NSArray enumerateObjectsWithBlock:]:

NSArray *people = @[
                     @{ @"name": @"Bob", @"city": @"Boston" },
                     @{ @"name": @"Rob", @"city": @"Cambridge" },
                     @{ @"name": @"Robert", @"city": @"Somerville" }
                  ];
// per the original question
NSArray *names = [people mapObjectsUsingBlock:^(id obj, NSUInteger idx) {
    return obj[@"name"];
}];
// (Bob, Rob, Robert)

// you can do just about anything in a block
NSArray *fancyNames = [people mapObjectsUsingBlock:^(id obj, NSUInteger idx) {
    return [NSString stringWithFormat:@"%@ of %@", obj[@"name"], obj[@"city"]];
}];
// (Bob of Boston, Rob of Cambridge, Robert of Somerville)

Answer 2

我不知道Ruby的功能是什么,但我认为你正在寻找NSArray的-valueForKey实现:.这将发送-valueForKey:到数组的每个元素并返回结果数组.如果接收数组中的元素是NSDictionaries,-valueForKey:则几乎相同-objectForKey:.只要密钥不以一个开头,它就会工作@

Answer 3

总结所有其他答案:

Ruby(如问题所示):

array.map{|o| o.name}

Obj-C(带valueForKey):

[array valueForKey:@"name"];

Obj-C(带valueForKeyPath,参见KVC集合运算符):

[array valueForKeyPath:@"[collect].name"];

Obj-C(使用enumerateObjectsUsingBlock):

NSMutableArray *newArray = [NSMutableArray array];
[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
     [newArray addObject:[obj name]];
}];

Swift(带地图,见封闭)

array.map { $0.name }

并且,有几个库允许您以更多功能的方式处理数组. 建议Cocoa Pods安装其他库.

Answer 4

更新:如果您使用的是Swift,请参阅地图.

BlocksKit是一个选项:

NSArray *new = [stringArray bk_map:^id(NSString *obj) { 
    return [obj stringByAppendingString:@".png"]; 
}];

Underscore是另一种选择.有一个map功能,这是网站上的一个例子:

NSArray *tweets = Underscore.array(results)
    // Let's make sure that we only operate on NSDictionaries, you never
    // know with these APIs ;-)
    .filter(Underscore.isDictionary)
    // Remove all tweets that are in English
    .reject(^BOOL (NSDictionary *tweet) {
        return [tweet[@"iso_language_code"] isEqualToString:@"en"];
    })
    // Create a simple string representation for every tweet
    .map(^NSString *(NSDictionary *tweet) {
        NSString *name = tweet[@"from_user_name"];
        NSString *text = tweet[@"text"];

        return [NSString stringWithFormat:@"%@: %@", name, text];
    })
    .unwrap;

Answer 5

我认为valueForKeyPath是一个不错的选择.

坐在下面有非常酷的例子.希望它有所帮助.

http://kickingbear.com/blog/archives/9

一些例子:

NSArray *names = [allEmployees valueForKeyPath: @"[collect].{daysOff<10}.name"];
NSArray *albumCovers = [records valueForKeyPath:@"[collect].{artist like 'Bon Iver'}.<NSUnarchiveFromDataTransformerName>.albumCoverImageData"];