Re: [Haskell-cafe] Where is "minimumsBy"?

That is interesting. Is anybody aware of a more detailed justification of how lazy evaluation makes this happen? - chris On 09/26/2018 11:38 PM, Bob Ippolito wrote:

Haskell’s sort algorithm is linear complexity when only evaluating the front of the list. See also  https://ro-che.info/articles/2016-04-02-descending-sort-haskell which includes some measurements. 

On Wed, Sep 26, 2018 at 10:30 David Feuer mailto:david.feuer@gmail.com> wrote:

Laziness does not make the complexity work out fine. Sorting is still O(n log n), which isn't needed here.

On Wed, Sep 26, 2018, 10:22 AM Tom Ellis mailto:tom-lists-haskell-cafe-2017@jaguarpaw.co.uk> wrote:

Hopefully laziness makes the complexity work out fine.  Nonetheless I don't like relying on laziness for the correct complexity and it would still be nice to have an explicit version.

On Wed, Sep 26, 2018 at 10:13:21AM -0400, Brandon Allbery wrote: > Not exactly that, but you can use groupBy fst . sort, then the head of the > result list is your "minimumsBy" result. > > On Wed, Sep 26, 2018 at 6:28 AM Tom Ellis < > tom-lists-haskell-cafe-2017@jaguarpaw.co.uk mailto:tom-lists-haskell-cafe-2017@jaguarpaw.co.uk> wrote: > > Data.List.minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a > > > > > > https://www.stackage.org/haddock/lts-12.1/base-4.11.1.0/Data-List.html#v:min... > > > > but there are many cases where that's quite unhelpful.  Actually what we > > want is more like > > > >     minimumsBy :: ... => (a -> a -> Ordering) -> t a -> [a] > > > > There can be many distinct minimizers.  For example when I want to get the > > collection of the youngest people from [(Age, Person)] I want > > > >     minimumsBy (compare `on` fst) [(12, alice), (15, balaji), (12, cho)] > > > > to return > > > >     [(12, alice), (12, cho)] > > > > Does "minimumsBy" exist somewhere reasonably standard?  Hoogle doesn't > > throw > > up anything obvious > > > > > > https://www.stackage.org/lts-12.1/hoogle?q=%28a+-%3E+a+-%3E+Ordering%29+-%3E... _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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