Re: Re: Changing the Natural Sort Order

*To*: mathgroup at smc.vnet.net*Subject*: [mg49219] Re: [mg49192] Re: Changing the Natural Sort Order*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Thu, 8 Jul 2004 02:50:53 -0400 (EDT)*References*: <ccb5hr$ekg$1@smc.vnet.net> <200407070542.BAA24966@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

On 7 Jul 2004, at 14:42, Paul Abbott wrote: > *This message was transferred with a trial version of CommuniGate(tm) > Pro* > In article <ccb5hr$ekg$1 at smc.vnet.net>, > "David Park" <djmp at earthlink.net> wrote: > >> Is it possible to change the natural sort order of symbols that is >> used in >> Sort? >> >> I would like something like the following statement (that does not >> work). >> >> Assuming[d < b < c, Sort[{a, b, c, d, f}]] >> >> giving the desired output >> >> {a,d,b,c,f} >> >> I won't be sorting simple lists of symbols, but lists of similar, but >> unspecified, expressions that contain the symbols. For example... >> >> {h[x,g[a]], h[x,g[b]], h[x,g[c]], h[x,g[d]], h[x,g[f]]} >> >> which should give >> >> {h[x,g[a]], h[x,g[d]], h[x,g[b]], h[x,g[c]], h[x,g[f]]} >> >> Is there any way to do this? > > I cannot see a simple way (via OrderedQ) to change the sort order of > symbols. However, here is one way to achieve what you want: > > [1] Use Ordering to define a set of replacement rules for your symbols: > > OrderRule[l_] := Thread[l[[Ordering[l]]] -> l] > > For your example, > > OrderRule[{d, b, c}] > {b -> d, c -> b, d -> c} > > [2] If you would like to use ordering like d < b < c, you could > overload > OrderRule as follows: > > OrderRule[Unevaluated[Less[l__]]] := OrderRule[{l}] > > OrderRule[Unevaluated[Greater[l__]]] := OrderRule[Reverse[{l}]] > > [3] Then use Sort followed by OrderRule: > > Sort[{a, b, c, d, f}] /. OrderRule[d < b < c] > {a, d, b, c, f} > > Sort[{h[x,g[f]], h[x, g[d]], h[x, g[c]], h[x, g[b]], h[x, g[a]]}] /. > OrderRule[d < b < c] > > {h[x, g[a]], h[x, g[d]], h[x, g[b]], h[x, g[c]], h[x, g[f]]} > > Cheers, > Paul > > -- > Paul Abbott Phone: +61 8 9380 2734 > School of Physics, M013 Fax: +61 8 9380 1014 > The University of Western Australia (CRICOS Provider No 00126G) > 35 Stirling Highway > Crawley WA 6009 mailto:paul at physics.uwa.edu.au > AUSTRALIA http://physics.uwa.edu.au/~paul > > If this is indeede what David meant (just permuting the selected symbols, in this case b,c,d) than it is easy to define an ordering that will do this by slightly modifying your approach and using user defined ordering function rather than a replacement rule: orderRule = {d -> b, b -> c, c -> d}; orderedQ[{x_, y_}] := OrderedQ[{x, y} /. orderRule] Sort[{a,b,c,d,f},orderedQ[{#1,#2}]&] {a,d,b,c,f} etc. Sort[{h[x,g[f]],h[x,g[d]],h[x,g[c]],h[x,g[b]],h[x,g[a]]},orderedQ[{#1,#2 }]&] {h(x,g(a)),h(x,g(d)),h(x,g(b)),h(x,g(c)),h(x,g(f))} etc. Andrzej Kozlowski Chiba, Japan http://www.mimuw.edu.pl/~akoz/

**References**:**Re: Changing the Natural Sort Order***From:*Paul Abbott <paul@physics.uwa.edu.au>