#2659: Add sortBy and other *By functions
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Reporter: twanvl | Owner:
Type: proposal | Status: new
Priority: normal | Component: libraries/base
Version: 6.9 | Severity: normal
Keywords: | Testcase:
Architecture: Unknown/Multiple | Os: Unknown/Multiple
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Almost all uses of {{{sortBy}}} are of the form {{{sortBy (comparing
f)}}}, {{{sortBy (compare `on` f)}}} or an equivalent construction. I
propose that we add the more convenient function {{{sortOn}}} to
Data.List:
{{{
sortOn :: Ord b => (a -> b) -> [a] -> [a]
}}}
For consistency for the other `By` functions we should also add an `On`
equivalent:
{{{
nubOn :: Eq b => (a -> b) -> [a] -> [a]
deleteOn :: Eq b => (a -> b) -> a -> [a] -> [a]
deleteFirstsOn :: Eq b => (a -> b) -> [a] -> [a] -> [a]
unionOn :: Eq b => (a -> b) -> [a] -> [a] -> [a]
intersectOn :: Eq b => (a -> b) -> [a] -> [a] -> [a]
groupOn :: Eq b => (a -> b) -> [a] -> [[a]]
sortOn :: Ord b => (a -> b) -> [a] -> [a]
insertOn :: Ord b => (a -> b) -> a -> [a] -> [a]
maximumOn :: Ord b => (a -> b) -> [a] -> a
minimumOn :: Ord b => (a -> b) -> [a] -> a
}}}
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2659>
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