Re: finding positions of elements in a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg86854] Re: finding positions of elements in a list*From*: "Dana DeLouis" <dana.del at gmail.com>*Date*: Sun, 23 Mar 2008 01:04:02 -0500 (EST)

> I also tried Position but it wasn't clear to me if a pattern can be used for this. Hi. You have answers, but I see you were stuck on using "Position." Here's one way if you ever need to use it: pts = {{20, 109}, {21, 50}, {20, 110}, {22, 60}}; Position[pts, {___, n_} /; n > 80] {{1}, {3}} Extract[pts, %] {{20, 109}, {20, 110}} -- HTH :>) Dana DeLouis "PeterM" <metaxas at lps.u-psud.fr> wrote in message news:frt5e9$srg$1 at smc.vnet.net... > Hi. > > Having a few problems here with what I think should be a simple operation. I have a list as shown: > > 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. > > Problem is, I can't work out how to use Select to do this when each element in the list has an x and a y co-ordinate. If I split the list into x and y co-ordinates and searched for those y values greater than 80, I would have a list of those y-values but would not know the corresponding x-values. > > I also tried Position but it wasn't clear to me if a pattern can be used for this. > > Thanks in advance, Pete. >