Re: simple question about removing elements from a table

*To*: mathgroup at smc.vnet.net*Subject*: [mg122405] Re: simple question about removing elements from a table*From*: Pete Boardman <pete.boardman at mac.com>*Date*: Thu, 27 Oct 2011 06:33:28 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201110262137.RAA29967@smc.vnet.net>

On 26 Oct 2011, at 22:37, Michael B. Heaney wrote: > data={{-0.5, 0.0321787}, {-0.489, 0.0321691}, {-0.478, > 0.032211}, {-0.467, 0.0321723}, {-0.456, 0.0322448}, {-0.444, 0.0321498}, > {-0.433, 0.032132}, {-0.422, 0.0321804}, {-0.411, 0.0322158}, > {-0.4, 0.0320886}, {-0.233, 0.0320596}, {0.567, 0.00286087}, {0.578, > -0.00143633}, {0.589, -0.00592979}, {0.6, -0.0113609}} > I want to remove all of the elements that have a positive first number, to > get: > > datasubset={{-0.5, 0.0321787}, {-0.489, 0.0321691}, {-0.478, > 0.032211}, {-0.467, 0.0321723}, {-0.456, 0.0322448}, {-0.444, 0.0321498}, > {-0.433, 0.032132}, {-0.422, 0.0321804}, {-0.411, 0.0322158}, > {-0.4, 0.0320886}, {-0.233, 0.0320596}} > > How do I do this? I'm a newcomer to Mathematica, but this might be something I can answer... :) >From the help: Select[list,crit] picks out all elements Subscript[e, i] of list for which crit[Subscript[e, i]] is True. so you supply the list, followed by a function that selects the elements you want. Select[data, #[[1]] < 0 &] where [[1]] < 0 says the first element is less than 0, and & defines a function that is applied to every element of the list, ie the #. hth pete

**References**:**simple question about removing elements from a table***From:*"Michael B. Heaney" <mheaney@gmail.com>