Add nubSort and maximumOn/minimumOn

CHANGES.txt

@@ -1,5 +1,7 @@
 Changelog for Extra
 
+    Add maximumOn and minimumOn
+    #31, add nubSort, nubSortBy and nubSortOn
 1.6.2, released 2017-12-07
     Mark the partial functions with Partial
     Add Partial constraint

src/Data/List/Extra.hs

@@ -9,7 +9,7 @@ module Data.List.Extra(
     module Data.List,
     -- * String operations
     lower, upper, trim, trimStart, trimEnd, word1, line1,
-    -- * Splitting    
+    -- * Splitting
     dropEnd, takeEnd, splitAtEnd, breakEnd, spanEnd,
     dropWhileEnd, dropWhileEnd', takeWhileEnd,
     stripSuffix, stripInfix, stripInfixEnd,
@@ -21,6 +21,8 @@ module Data.List.Extra(
     groupSort, groupSortOn, groupSortBy,
     nubOrd, nubOrdBy, nubOrdOn,
     nubOn, groupOn, sortOn,
+    nubSort, nubSortBy, nubSortOn,
+    maximumOn, minimumOn,
     disjoint, allSame, anySame,
     repeatedly, for, firstJust,
     concatUnzip, concatUnzip3,
@@ -296,6 +298,13 @@ groupOn f = groupBy ((==) `on2` f)
 nubOn :: Eq b => (a -> b) -> [a] -> [a]
 nubOn f = map snd . nubBy ((==) `on` fst) . map (\x -> let y = f x in y `seq` (y, x))
 
+-- | A version of 'maximum' where the comparison is done on some extracted value.
+maximumOn :: Ord b => (a -> b) -> [a] -> a
+maximumOn f = maximumBy (compare `on` f)
+
+-- | A version of 'minimum' where the comparison is done on some extracted value.
+minimumOn :: Ord b => (a -> b) -> [a] -> a
+minimumOn f = minimumBy (compare `on` f)
 
 -- | A combination of 'group' and 'sort'.
 --
@@ -548,6 +557,29 @@ chunksOf i xs | i <= 0 = error $ "chunksOf, number must be positive, got " ++ sh
 chunksOf i xs = repeatedly (splitAt i) xs
 
 
+-- | /O(n log n)/. The 'nubSort' function sorts and removes duplicate elements from a list.
+-- In particular, it keeps only the first occurrence of each element.
+--
+-- > nubSort "this is a test" == " aehist"
+-- > \xs -> nubSort xs == nub (sort xs)
+nubSort :: Ord a => [a] -> [a]
+nubSort = nubSortBy compare
+
+-- | A version of 'nubSort' which operates on a portion of the value.
+--
+-- > nubSortOn length ["a","test","of","this"] == ["a","of","test"]
+nubSortOn :: Ord b => (a -> b) -> [a] -> [a]
+nubSortOn f = nubSortBy (compare `on` f)
+
+-- | A version of 'nubSort' with a custom predicate.
+--
+-- > nubSortBy (compare `on` length) ["a","test","of","this"] == ["a","of","test"]
+nubSortBy :: (a -> a -> Ordering) -> [a] -> [a]
+nubSortBy cmp = f . sortBy cmp
+    where f (x1:x2:xs) | cmp x1 x2 == EQ = f (x1:xs)
+          f (x:xs) = x : f xs
+          f [] = []
+
 -- | /O(n log n)/. The 'nubOrd' function removes duplicate elements from a list.
 -- In particular, it keeps only the first occurrence of each element.
 -- Unlike the standard 'nub' operator, this version requires an 'Ord' instance

src/Extra.hs

@@ -23,7 +23,7 @@ module Extra {-# DEPRECATED "This module is provided as documentation of all new
     modifyIORef', writeIORef', atomicModifyIORef', atomicWriteIORef, atomicWriteIORef',
     -- * Data.List.Extra
     -- | Extra functions available in @"Data.List.Extra"@.
-    lower, upper, trim, trimStart, trimEnd, word1, line1, dropEnd, takeEnd, splitAtEnd, breakEnd, spanEnd, dropWhileEnd, dropWhileEnd', takeWhileEnd, stripSuffix, stripInfix, stripInfixEnd, wordsBy, linesBy, breakOn, breakOnEnd, splitOn, split, chunksOf, list, uncons, unsnoc, cons, snoc, drop1, mconcatMap, groupSort, groupSortOn, groupSortBy, nubOrd, nubOrdBy, nubOrdOn, nubOn, groupOn, sortOn, disjoint, allSame, anySame, repeatedly, for, firstJust, concatUnzip, concatUnzip3, zipFrom, zipWithFrom, replace, merge, mergeBy,
+    lower, upper, trim, trimStart, trimEnd, word1, line1, dropEnd, takeEnd, splitAtEnd, breakEnd, spanEnd, dropWhileEnd, dropWhileEnd', takeWhileEnd, stripSuffix, stripInfix, stripInfixEnd, wordsBy, linesBy, breakOn, breakOnEnd, splitOn, split, chunksOf, list, uncons, unsnoc, cons, snoc, drop1, mconcatMap, groupSort, groupSortOn, groupSortBy, nubOrd, nubOrdBy, nubOrdOn, nubOn, groupOn, sortOn, nubSort, nubSortBy, nubSortOn, maximumOn, minimumOn, disjoint, allSame, anySame, repeatedly, for, firstJust, concatUnzip, concatUnzip3, zipFrom, zipWithFrom, replace, merge, mergeBy,
     -- * Data.Tuple.Extra
     -- | Extra functions available in @"Data.Tuple.Extra"@.
     first, second, (***), (&&&), dupe, both, fst3, snd3, thd3,

test/TestGen.hs

@@ -194,6 +194,10 @@ tests = do
     testGen "chunksOf 3 \"mytest\"  == [\"myt\",\"est\"]" $ chunksOf 3 "mytest"  == ["myt","est"]
     testGen "chunksOf 8 \"\"        == []" $ chunksOf 8 ""        == []
     testGen "chunksOf 0 \"test\"    == undefined" $ erroneous $ chunksOf 0 "test"
+    testGen "nubSort \"this is a test\" == \" aehist\"" $ nubSort "this is a test" == " aehist"
+    testGen "\\xs -> nubSort xs == nub (sort xs)" $ \xs -> nubSort xs == nub (sort xs)
+    testGen "nubSortOn length [\"a\",\"test\",\"of\",\"this\"] == [\"a\",\"of\",\"test\"]" $ nubSortOn length ["a","test","of","this"] == ["a","of","test"]
+    testGen "nubSortBy (compare `on` length) [\"a\",\"test\",\"of\",\"this\"] == [\"a\",\"of\",\"test\"]" $ nubSortBy (compare `on` length) ["a","test","of","this"] == ["a","of","test"]
     testGen "nubOrd \"this is a test\" == \"this ae\"" $ nubOrd "this is a test" == "this ae"
     testGen "nubOrd (take 4 (\"this\" ++ undefined)) == \"this\"" $ nubOrd (take 4 ("this" ++ undefined)) == "this"
     testGen "\\xs -> nubOrd xs == nub xs" $ \xs -> nubOrd xs == nub xs