Re: Maximum in a list
- To: mathgroup at smc.vnet.net
- Subject: [mg97240] Re: [mg97209] Maximum in a list
- From: DrMajorBob <btreat1 at austin.rr.com>
- Date: Mon, 9 Mar 2009 01:03:31 -0500 (EST)
- References: <200903081050.FAA21521@smc.vnet.net>
- Reply-to: drmajorbob at bigfoot.com
Here's a simple method: mylist = {{1, 2}, {3, 4}, {8, 3}}; select[s_List] := s[[Ordering[s[[All, 2]], -1]]] mylist = RandomInteger[{1, 4}, {50, 2}] select@mylist {{3, 3}, {1, 2}, {4, 1}, {1, 3}, {4, 3}, {1, 4}, {1, 2}, {1, 4}, {1, 3}, {3, 4}, {4, 2}, {3, 1}, {2, 1}, {3, 3}, {3, 4}, {4, 2}, {4, 4}, {2, 1}, {4, 2}, {4, 3}, {1, 3}, {3, 2}, {2, 2}, {4, 2}, {2, 4}, {1, 4}, {4, 1}, {4, 3}, {3, 1}, {3, 1}, {3, 4}, {2, 1}, {3, 3}, {4, 1}, {3, 1}, {4, 3}, {3, 4}, {4, 4}, {2, 1}, {4, 3}, {3, 1}, {4, 2}, {1, 1}, {3, 2}, {1, 2}, {2, 1}, {4, 1}, {1, 2}, {3, 3}, {1, 4}} {{1, 4}} "select" returns the LAST element for which the second element is maximum, which may not be what you want. If you want the FIRST such element, change "select" to Clear[select] select[s_List] := s[[Ordering[Reverse@s[[All, 2]], -1]]] select@mylist {{1, 2}} For either of those, you could add First@ to get only the element, rather than a list with only that element: Clear[select] select[s_List] := First@s[[Ordering[Reverse@s[[All, 2]], -1]]] select@mylist {1, 2} If you want ALL pairs for which the second element is maximum, then: Clear[select] select[s_List] := Extract[s, Position[s[[All, 2]], Max@s[[All, 2]]]] select@mylist {{1, 4}, {1, 4}, {3, 4}, {3, 4}, {4, 4}, {2, 4}, {1, 4}, {3, 4}, {3, 4}, {4, 4}, {1, 4}} If you want the same thing without repeats, you can do it with: Clear[select] select[s_List] := Union@Extract[s, Position[s[[All, 2]], Max@s[[All, 2]]]] select@mylist {{1, 4}, {2, 4}, {3, 4}, {4, 4}} or Clear[select, unsortedUnion] unsortedUnion[s_List] := Tally[s][[All, 1]] select[s_List] := unsortedUnion@Extract[s, Position[s[[All, 2]], Max@s[[All, 2]]]] select@mylist {{1, 4}, {3, 4}, {4, 4}, {2, 4}} or Clear[select] select[s_List] := DeleteDuplicates@Extract[s, Position[s[[All, 2]], Max@s[[All, 2]]]] select@mylist {{1, 4}, {3, 4}, {4, 4}, {2, 4}} Bobby On Sun, 08 Mar 2009 05:50:59 -0500, pacotomi <pacotomi at orange.fr> wrote: > Hi, > Suppose a list > > mylist={{1,2},{3,4},{8,3}} > > I would like to extract the element {i,j} of mylist for which j is max > (here, it is the second one {3,4}). > > Somebody could help me, please? > > Pacotomi > > > > -- DrMajorBob at bigfoot.com
- References:
- Maximum in a list
- From: pacotomi@orange.fr (pacotomi)
- Maximum in a list