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Re: Conditional drop of list elements

• To: mathgroup at smc.vnet.net
• Subject: [mg63591] Re: Conditional drop of list elements
• From: Paul <gleam at flashmail.com>
• Date: Fri, 6 Jan 2006 05:24:37 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

> Hi guys,
> 
> I need your assistance by the following problem:
> 
> list1 = {{0,A,A,A}, {1,B,B,B}, {0,C,C,C}, {1,D,D,D},
> {1,F,F,F},
> {0,G,G,G}, {0,H,H,H}}
> 
> Every 1st element of the each sublist should be
> checked. Is the first
> element a ZERO, this sublist should be removed from
> the list. If it is
> a ONE - this sublist remains in the list.
> 
> In this example the output should be:
> 
> {{1,B,B,B}, {1,D,D,D},{1,F,F,F}}
> 
> Thanks for your help!
> 
> LZ


Hello LectorZ,

I believe that Pick is the better function for this application, if you are using Mathematica version 5.1 or later.

Please consider:

In[1]:=
list1=Table[Random[Integer], {250000}, {5}];

In[2]:=
AbsoluteTiming[Pick[list1, list1[[All, 1]], 1];]

Out[2]=
{0.1875000 Second, Null}

In[3]:=
AbsoluteTiming[Cases[list1, {1, ___}];]

Out[3]=
{0.3437500 Second, Null}

In[4]:=
AbsoluteTiming[DeleteCases[list1, {0, ___}];]

Out[4]=
{0.4218750 Second, Null}

In[5]:=
AbsoluteTiming[list1 /. {0, ___} :> Sequence[];]

Out[5]=
{0.5000000 Second, Null}

In[6]:=
AbsoluteTiming[Select[list1, #[[1]] == 1 &];]

Out[6]=
{0.8906250 Second, Null}



Paul

• Follow-Ups:
  • Re: Re: Conditional drop of list elements
    • From: "Carl K. Woll" <carlw@wolfram.com>