Re: Delete elements from list..

*To*: mathgroup at smc.vnet.net*Subject*: [mg116683] Re: Delete elements from list..*From*: "Maarten van der Burgt" <Maarten.VanDerBurgt at kla-tencor.com>*Date*: Thu, 24 Feb 2011 06:20:31 -0500 (EST)

Hallo, Thanks everybody who replied to my questions. The real problem I have is just a bit more complex than my simplified example. My list is in fact a numerical 2D list like mylist1 == {{x_0, y_0}, {x_1,y_1},... {x_i, y_i}, ...{x_N, y_N}}. The xi are strictly increasing and the yi should be as well. Due to some measurement errors it can happen that this is not the case. I simply want to delete the {xi, yi} pairs where y_i <== y_i-1. That way I end up with a list, mylist2, where also the y_i are strictly increasing. (that way I can make an Interpolation[Reverse/@mylist2] in order to have a function x_i(y_i)). I have not had the time to study your answers in this view, but from a first look and the variety of the answers it seems that there is definitely something which should help. Thanks for your help. Maarten -----Original Message----- From: Achilleas Lazarides [mailto:achilleas.lazarides at gmx.com] Sent: Wednesday, 23 February, 2011 11:22 To: mathgroup at smc.vnet.net Subject: [mg116683] [mg116653] Re: Delete elements from list.. Do you really want the resulting list to only have increasing elements? then something like Module[{tmpl == mylist[[1]]}, Scan[(If[# > tmpl, Sow[#]; tmpl == #]) &, mylist]; // Reap] should work (except that it eats the first element). If you actually meant that you want to delete any element that is not strictly larger than the previous, then Module[{tmpl == mylist[[1]]}, Scan[(If[# > tmpl, Sow[#]]; tmpl == #) &, mylist]; // Reap] (which again eats the first element). On Feb22, 2011, at 1:30 AM, Maarten van der Burgt wrote: > Hallo, > > I have a list like: > > mylist == {1, 2, 3, 4, 5, 6, 4, 5, 7, 8, 9} > > I want to delete any element which is not strictly larger than the > previous element, until my new list has only increasing values. > > This means in mylist above I want to delete the 4 and the 5 at position > 7 and 8. > > Any elegant and fast way for doing this? > > In practice I want to do this for a large amount (1000) of very large > lists (1000). So speed is important. > > Thanks for your help. > > Maarten