Re: Position function
- To: mathgroup at smc.vnet.net
- Subject: [mg55560] Re: [mg55549] Position function
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Wed, 30 Mar 2005 03:20:55 -0500 (EST)
- References: <200503290842.DAA07267@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On 29 Mar 2005, at 10:42, 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}}
For example:
In[2]:=
a = {{1, 3, 1, 2, 1}, {5, 6, 1, 1, 3, 1}};
In[3]:=
Split[Position[a, 1], #1[[1]] == #2[[1]] & ] /.
(l_)?VectorQ :> Last[l]
Out[3]=
{{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}
In[4]:=
Position[a, 1] /.
(l_)?VectorQ :> Last[l]
Out[4]=
{1,3,5,3,4,6}
Andrzej Kozlowski
Chiba, Japan
http://www.akikoz.net/andrzej/index.html
http://www.mimuw.edu.pl/~akoz/
- References:
- Position function
- From: konstantpi@mail15.com
- Position function