flatten

Given I have an array: $array = array( 'a' => array( 'b' => array( 'c' => 'hello', ), ), 'd' => array( 'e' => array( 'f' => 'world', ), ), ); I want to "flatten" it to a single dimension look-up of references, concatenating keys with a delimiter ( in the case of this example, a forward slash / ) Performing a var_dump() on a successful output would yield: ( note all the references ) array(6) { ["a"]=> &array(1) { ["b"]=> &array(1) { ["c"]=> &string(5) "hello" } } ["a/b"]=> &array(1) { ["c"]=> &string(5) "hello" } ["a/b/c"]=> &string(5) "hello" ["d"]=> &array(1) { ["e"]=> &array(1) { ["f"]=>

I am a beginner interested in Haskell, and I have been trying to implement the flatmap (>>=) on my own to better understand it. Currently I have flatmap :: (t -> a) -> [t] -> [a] flatmap _ [] = [] flatmap f (x:xs) = f x : flatmap f xs which implements the "map" part but not the "flat". Most of the modifications I make result in the disheartening and fairly informationless Occurs check: cannot construct the infinite type: a = [a] When generalising the type(s) for `flatmap' error. What am I missing? An error like this happens when the type signature you specify does not match the actual type of

As you may know, a DataFrame can contain fields which are complex types, like structures (StructType) or arrays (ArrayType). You may need, as in my case, to map all the DataFrame data to a Hive table, with simple type fields (String, Integer...). I've been struggling with this issue for a long time, and I've finally found a solution I want to share. Also, I'm sure it could be improved, so feel free to reply with your own suggestions. It's based on this thread , but also works for ArrayType elements, not only StructType ones. It is a tail recursive function which receives a DataFrame, and

In the context of a discussion in the comments of this question it was mentioned that while concatenating a sequence of strings simply takes ''.join([str1, str2, ...]) , concatenating a sequence of lists would be something like list(itertools.chain(lst1, lst2, ...)) , although you can also use a list comprehension like [x for y in [lst1, lst2, ...] for x in y] . What surprised me is that the first method is consistently faster than the second: import random import itertools random.seed(100) lsts = [[1] * random.randint(100, 1000) for i in range(1000)] %timeit [x for y in lsts for x in y] # 39

Is there a flatten method in Guava - or an easy way to convert an Iterable<Iterable<T>> to an Iterable<T> ? I have a Multimap<K, V> [sourceMultimap] and I want to return all values where the key matches some predicate [keyPredicate]. So at the moment I have: Iterable<Collection<V>> vals = Maps.filterKeys(sourceMultimap.asMap(), keyPredicate).values(); Collection<V> retColl = ...; for (Collection<V> vs : vals) retColl.addAll(vs); return retColl; I've looked through the Guava docs, but nothing jumped out. I am just checking I've not missed anything. Otherwise, I'll extract my three lines into a