NSArray of united Arrays - iphone

Question

I have an NSArray of objects called MMPlace, which has NSArray of MMProduct objects.
How do I get a united NSArray of all MMProduct objects that my Array of MMPlace object contains? Something like NSArray *arr = [array valueForKeyPath:#"#unionOfObjects.products"]; would be nice, though this specific example doesn't work.

Answer 1

You can do this with #unionOfArrays. The bit you were missing is that because the arrays are directly nested, the key on the right of the collection operator must be self:
NSArray *nestedValues = #[#[#1, #2, #3], #[#4, #5, #6]]
NSArray *flattenedValues = [nestedValues valueForKeyPath:#"#unionOfArrays.self"];
// flattenedValues contains #[#1, #2, #3, #4, #5, #6]

Answer 2

Create an NSMutableArray, loop through your original array and call addObjectsFromArray: with each subarray.

Answer 3

I don't think there is an off-the-shelf method that does what you need, but you can easily "flatten" your array in a for loop, and hide the method in a category:
Edit: added a category.
#interface NSArray (flatten)
-(NSArray*) flattenArray;
#end
#implementation NSArray (flatten)
-(NSArray*) flattenArray {
// If inner array has N objects on average, multiply count by N
NSMutableArray *res = [NSMutableArray arrayWithCapacity:self.count];
for (NSArray *element in self) {
[res addObjectsFromArray:element];
}
return res;
}
#end

Answer 4

For this task there is the #unionOfArrays collection operator.
http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/KeyValueCoding/Articles/CollectionOperators.html#//apple_ref/doc/uid/20002176-BAJEAIEE

Answer 5

Here is how I implemented a "flatten" category method that will work on any tree structure. It will take a tree of arbitrary depth and merge it into one long array in order.
- (NSArray *) flattenWithBlock:(NSArray *(^)(id obj))block {
NSMutableArray *newItems = [NSMutableArray array];
for(id subObject in self)
{
if([subObject isKindOfClass:[NSArray class]])
{
[newItems addObjectsFromArray:[subObject flatten:block]];
}
else
[newItems addObject:subObject];
}
return newItems;
}
You could then write a convenience category method which handles the case you described above. This wrapper method will flatten a nd array into a 1d array.
- (NSArray *) flattenArray {
NSArray *newItems = [self flattenWithBlock:^NSArray *(id obj) {
return obj;
}];
return newItems;
}

Answer 6

#interface NSArray (Flatten)
-(NSArray*)flattenedArray;
#end
#implementation NSArray (Flatten)
-(NSArray*)flattenedArray {
NSMutableArray *result = [NSMutableArray arrayWithCapacity:self.count];
for (id thing in self) {
if ([thing isKindOfClass:[NSArray class]]) {
[result addObjectsFromArray:[(NSArray*)thing flattenedArray]];
} else {
[result addObject:thing];
}
}
return [NSArray arrayWithArray:result];
}
#end