javascript JS 的`map()` 函数的Objective-C 等价物是什么？
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What's the Objective-C equivalent of JS's `map()` function?
提问by Moshe
What's the Objective-C equivalent of JS's map()function? Would I just use NSFastEnumeration and apply the function myself?
JSmap()函数的 Objective-C 等价物是什么？我会只使用 NSFastEnumeration 并自己应用该函数吗？
回答by mipadi
You can use NSArray's enumerateObjectsUsingBlock:if you're on OS X 10.6 or iOS 4.:
如果您使用NSArray的enumerateObjectsUsingBlock:是 OS X 10.6 或 iOS 4，则可以使用's ：
NSMutableArray *mapped = [NSMutableArray arrayWithCapacity:[array count]];
[array enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
id mapObj = DoSomethingToObject(obj);
[mapped addObject:mapObj];
}];
(Shameless but relevant plug: I have a libraryfor OS X and iOS that adds map and other similar functionality to NSArrayand NSSet.)
（无耻的，但相关的插件：我有一个库为OS X和iOS，增加了地图和其他类似的功能NSArray和NSSet。）
回答by Dave DeLong
It depends. If you have, say, an array of objects, and these objects have a URLproperty (for example), then you can do:
这取决于。如果你有一个对象数组，并且这些对象有一个URL属性（例如），那么你可以这样做：
NSArray * urls = [myArray valueForKey:@"URL"];
Likewise, if you can trigger the behavior of the objects in question via a single message that takes 0 or 1 parameters, you can do:
同样，如果您可以通过带有 0 或 1 个参数的单个消息触发相关对象的行为，您可以执行以下操作：
[myArray makeObjectsPerformSelector:@selector(doFoo)];
//or:
[myArray makeObjectsPerformSelector:@selector(doFooWithBar:) withObject:aBar];
For anything beyond that, you'll have to iterate over the objects yourself. You can use a for()loop, a for(in)loop, or something like -enumerateObjectsUsingBlock:, etc.
对于除此之外的任何事情，您必须自己迭代对象。您可以使用for()循环、for(in)循环或类似的东西等-enumerateObjectsUsingBlock:。
回答by Jonathan Grynspan
You do it yourself. There is no single method equivalent to what you want.
你自己做。没有与您想要的等效的单一方法。
Edit: For those downvoting, this was the correct answer at the time (three years ago) and still is for Objective-C, but Swift does have a map()function.
编辑：对于那些投反对票的人，这是当时（三年前）的正确答案，并且仍然适用于 Objective-C，但 Swift 确实有一个map()功能。
回答by Hai Feng Kao
Check BlocksKit, it provides map, reduce and filer for NSArray.
检查BlocksKit，它为 NSArray 提供 map、reduce 和 filer。
- (NSArray *)map:(BKTransformBlock)block;
- (id)reduce:(id)initial withBlock:(BKAccumulationBlock)block;
- (NSArray *)select:(BKValidationBlock)block;
- (NSArray *)map:(BKTransformBlock)block;
- (id)reduce:(id)initial withBlock:(BKAccumulationBlock)block;
- (NSArray *)select:(BKValidationBlock)block;
回答by Nicolas Manzini
Category function for NSArrayan alternative
NSArray的分类函数的另一种选择
- (NSArray *)map:(id(^)(id, BOOL *))block {
NSMutableArray * array = [NSMutableArray array];
[self enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
id newObject = block(obj,stop);
if (newObject == nil) {
newObject = [NSNull null];
}
[array addObject:newObject];
}];
return array.copy;
}
Category function for NSMutableArrayan alternative
NSMutableArray的分类函数替代
- (NSMutableArray *)map:(id(^)(id))block {
NSEnumerator * enumerator = ((NSArray *)self.copy).objectEnumerator;
id obj; NSUInteger idx = 0;
while ((obj = enumerator.nextObject)) {
self[idx] = block(obj) ?: [NSNull null];
idx++;
}
return self;
}
