Re: Position on a List

*To*: mathgroup at smc.vnet.net*Subject*: [mg13188] Re: Position on a List*From*: "Allan Hayes" <hay at haystack.demon.cc.uk>*Date*: Mon, 13 Jul 1998 07:42:37 -0400*References*: <6mqa63$2qt@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Idoia Aguirre wrote: | | When I do: Position[{1/A, A}, A] | | I obtain: {{1,1},{2}} | | But I would like to obtain only : {{2}} | Several correspondents have pointed out that specifying the level does the trick: Position[{1/A, A}, A, {1}] {{2}} Position has two other controls that are often useful: 1) the maximum number of positions to return: Position[{1/A, A, A, A}, A, {1}] {{2}, {3}, {4}} Position[{1/A, A, A, A}, A, {1},2] {{2}, {3}} 2) Whether to look inside heads: Position[A[1/A, A, A],A, {1}] {{0}, {2}, {3}} Position[A[1/A, A, A],A, {1}, Heads->False] {{2}, {3}} Using all possibilites give us three optiona controls: Position[expression, level specification (default {0,Infinity}), maxnumber of positions to return (default Infinity), Heads->True (default) or Heads-> False ] ------------------------------------------------------------- Allan Hayes Training and Consulting Leicester UK http://www.haystack.demon.co.uk hay at haystack.demon.co.uk voice: +44 (0)116 271 4198 fax: +44(0)116 271 8642