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MathGroup Archive 2005

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Re: Position function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55564] Re: [mg55549] Position function
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Wed, 30 Mar 2005 03:20:58 -0500 (EST)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

a={{1,3,1,2,1},{5,6,1,1,3,1}};

Flatten[Position[#,1]]&/@a

{{1, 3, 5}, {3, 4, 6}}

Last/@Position[a,1]

{1, 3, 5, 3, 4, 6}


Bob Hanlon

> 
> From: konstantpi at mail15.com
To: mathgroup at smc.vnet.net
> Date: 2005/03/29 Tue AM 03:42:32 EST
> To: mathgroup at smc.vnet.net
> Subject: [mg55564] [mg55549] Position function
> 
> 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}}
> 
> 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}
> thanks
> konst.
> 
> 


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