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MathGroup Archive 2005

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Position function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55549] Position function
  • From: konstantpi at mail15.com
  • Date: Tue, 29 Mar 2005 03:42:32 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

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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