Convert a list of things into a list of sublists
This function already exists, this is group :: Eq a => [a] -> [[a]]
:
Prelude> import Data.List(group)
Prelude Data.List> group [1,2,2,1,3,3,3,2,2,1,1,4]
[[1],[2,2],[1],[3,3,3],[2,2],[1,1],[4]]
It is often fruitful to check Hoogle when you're looking for a function that might already exist. Because you can search by type, you don't have to know what the function is called. And even if it doesn't exist, it's a good exercise because it makes you think about what type it should have.
Here, the simple type to start with is [a] -> [[a]]
, but this search yields no results. On reflection this makes sense: you can't split a list of arbitrary objects without some way to compare them.
There are a few ways you might think of to compare list items. One obvious one, since you want to group items that are equal, is Eq. So you might try a search for Eq a => [a] -> [[a]]
, and this in fact yields group
. You might similarly try Ord a
instead, since Ord is another way to compare things, but this yields no results.
Lastly you might try the most general thing possible: take in a predicate function dictating where to split the list. A search for (a -> a -> Bool) -> [a] -> [[a]]
yields groupBy
, which is another reasonable way of achieving your goal, though in fact more general than necessary.