Re: Select only certain sublists matching criteria
- To: mathgroup at smc.vnet.net
- Subject: [mg111004] Re: Select only certain sublists matching criteria
- From: Patrick Scheibe <pscheibe at trm.uni-leipzig.de>
- Date: Fri, 16 Jul 2010 05:19:04 -0400 (EDT)
Hi,
yes you can use Select. But with pattern matching and Cases it is
readable too:
l = {{0, -4, 2.283}, {0.5, -4, 2.282}, {1, -4, 2.280}, {1.5, -4,
2.276}, {2, -4, 2.271}, {2.5, -4, 2.264}, {3, -4,
2.255}, {3.5, -4, 2.242}};
Cases[l, {_, _, _?(Abs[# - 2.25] < 0.01 &)}]
Select[l, Abs[#[[3]] - 2.25] < 0.01 &]
Cheers
Patrick
On Thu, 2010-07-15 at 03:09 -0400, Chris Poole wrote:
> I have a list like this:
> {{0, -4, 2.283}, {0.5, -4, 2.282}, {1, -4, 2.280}, {1.5, -4,
> 2.276}, {2, -4, 2.271}, {2.5, -4, 2.264}, {3, -4, 2.255}, {3.5, -4,
> 2.242}}
>
> I want to look at each list of 3 numbers, and keep only the lists where the third item in each list fits some criteria.
>
> I can do something like this:
> Select[{2, 15, 1, 16, 17}, Abs[3 - #] < 3 &]
>
> But it only works for flat lists.
>
> For example, I want only the lists where the third item is around 2.25 +- 0.001. Something like that.
>
> I can work out how to get Select to operate on the 3rd item of each sublist, but not how to then keep that entire list.
>
> If anyone has any ideas, they are much appreciated.
>