Data.Vector.Split

Documentation

chunksOf :: Vector v a => Int -> v a -> [v a]

chunksOf n splits a vector into length-n pieces. The last piece will be shorter if n does not evenly divide the length of the vector. If n <= 0, chunksOf n l returns an infinite list of empty vectors. For example:

Note that chunksOf n [] is [], not [[]]. This is intentional, and is consistent with a recursive definition of chunksOf; it satisfies the property that

chunksOf n xs ++ chunksOf n ys == chunksOf n (xs ++ ys)

whenever n evenly divides the length of xs.

splitPlaces :: Vector v a => [Int] -> v a -> [v a]

Split a vector into chunks of the given lengths. For example:

splitPlaces [2,3,4] [1..20] == [[1,2],[3,4,5],[6,7,8,9]]
splitPlaces [4,9] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]
splitPlaces [4,9,3] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]

If the input vector is longer than the total of the given lengths, then the remaining elements are dropped. If the vector is shorter than the total of the given lengths, then the result may contain fewer chunks than requested, and the last chunk may be shorter than requested.

splitPlacesBlanks :: Vector v a => [Int] -> v a -> [v a]

Split a vector into chunks of the given lengths. Unlike splitPlaces, the output list will always be the same length as the first input argument. If the input vector is longer than the total of the given lengths, then the remaining elements are dropped. If the vector is shorter than the total of the given lengths, then the last several chunks will be shorter than requested or empty. For example:

splitPlacesBlanks [2,3,4] [1..20] == [[1,2],[3,4,5],[6,7,8,9]]
splitPlacesBlanks [4,9] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]
splitPlacesBlanks [4,9,3] [1..10] == [[1,2,3,4],[5,6,7,8,9,10],[]]

Notice the empty list in the output of the third example, which differs from the behavior of splitPlaces.

chop :: Vector v a => (v a -> (b, v a)) -> v a -> [b]

A useful recursion pattern for processing a list to produce a new list, often used for "chopping" up the input list. Typically chop is called with some function that will consume an initial prefix of the list and produce a value and the rest of the list.

For example, many common Prelude functions can be implemented in terms of chop:

group :: (Eq a) => [a] -> [[a]]
group = chop (\ xs@(x:_) -> span (==x) xs)

words :: String -> [String]
words = filter (not . null) . chop (span (not . isSpace) . dropWhile isSpace)

divvy :: Vector v a => Int -> Int -> v a -> [v a]

Divides up an input vector into a set of subvectors, according to n and m input specifications you provide. Each subvector will have n items, and the start of each subvector will be offset by m items from the previous one.

divvy 5 5 [1..20] == [[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15],[16,17,18,19,20]]

In the case where a source vector's trailing elements do no fill an entire subvector, those trailing elements will be dropped.

divvy 5 2 [1..10] == [[1,2,3,4,5],[3,4,5,6,7],[5,6,7,8,9]]

As an example, you can generate a moving average over a vector of prices:

type Prices = [Float]
type AveragePrices = [Float]

average :: [Float] -> Float
average xs = sum xs / (fromIntegral $ length xs)

simpleMovingAverage :: Prices -> AveragePrices
simpleMovingAverage priceList =
  map average divvyedPrices
    where divvyedPrices = divvy 20 1 priceList

module Data.Vector.Split.Internal