Re: Position function

*To*: mathgroup at smc.vnet.net*Subject*: [mg55592] Re: Position function*From*: dh <dh at metrohm.ch>*Date*: Wed, 30 Mar 2005 03:22:23 -0500 (EST)*References*: <d2b4q9$77c$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hello Konstatin, konstantpi at mail15.com wrote: > suppose i have a List: > a={{1,3,1,2,1},{5,6,1,1,3,1}} > how i could know the positions of "1" in every sublist , i could use Position[a > [[1]],1] and Position[a[[2]],1] > but i want a one formula to give me {{1,3,5},{3,4,6}} Position does just that. You only have to arrange the output to your taste, what can be done by Cases: a = {{1, 3, 1, 2, 1}, {5, 6, 1, 1, 3, 1}}; p = Position[a, 1]; Cases[p, {1, x_} -> x] gives: {1, 3, 5} or all sublist in one go, using Map and a pure function: Flatten @ Position [#, 1] & /@ a gives: {{1, 3, 5}, {3, 4, 6}} > > the second question: > using Position[a,1] will give: > {{1, 1}, {1, 3}, {1, 5}, {2, 3}, {2, 4}, {2, 6}} > in general how to extract only the second item from every sublist so the output > will be; > {1,3,5,3,4,6} t={{1, 1}, {1, 3}, {1, 5}, {2, 3}, {2, 4}, {2, 6}}; t[[All,2]] gives: {1, 3, 5, 3, 4, 6} Sincerely, Daniel