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RE: finding positions of elements in a list

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86784] RE: [mg86761] finding positions of elements in a list
  • From: "David Annetts" <davidannetts at aapt.net.au>
  • Date: Thu, 20 Mar 2008 05:50:35 -0500 (EST)
  • References: <200803200755.CAA29380@smc.vnet.net>

Hi Peter,

> 
> mylist={{20, 109}, {20, 110}, {20, 111}, {21, 105}, {21, 
> 106}, {21, 107},...}
> 
> It's a list of {x,y} co-ordinates of some data points I'm analysing.
> 
> I want to create a new list which contains only those data 
> points whose y co-ordinate is greater than 80 ie. mylist[[n,2]]>80.

You can use Select.  You want to select everything based on the second part
of every element in the list.

Given

	mylist = {{20, 109}, {20, 110}, {20, 111}, {21, 105}, {21, 106},
{21, 107}};
	
The command 

	Select[mylist, #[[2]] > 109 &]

gets everything with a y-coordinate > 109.  

Regards,

Dave.

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