Notice: On March 31, it was **announced** that Statalist is moving from an email list to a **forum**. The old list will shut down on April 23, and its replacement, **statalist.org** is already up and running.

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

From |
Nick Cox <njcoxstata@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: programatically dropping variables that don't actually vary |

Date |
Thu, 9 Aug 2012 20:12:47 +0100 |

In principle, many variables could have mean 0. A safer test is that if r(min) == 0 and r(max) == 0 Nick On Thu, Aug 9, 2012 at 8:03 PM, Sarah Edgington <sedging@ucla.edu> wrote: > Jenn, > There are a variety of ways you might want to do this. What I would do is > something like the following: > > foreach var of varlist dummy1-dummyn { > sum `var', meanonly > if r(mean)==0 { > drop `var' > } > } > > This cycles through each of your variables (substitute your actual variable > list for "dummy1-dummyn"). For reach variable it calculates the mean. The > drop statement in the if loop only gets executed if the value stored in > r(mean) is 0. > > -Sarah > > > -----Original Message----- > From: owner-statalist@hsphsun2.harvard.edu > [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Earl, Jennifer > Suzanne - (jenniferearl) > Sent: Thursday, August 09, 2012 11:46 AM > To: statalist@hsphsun2.harvard.edu > Subject: st: programatically dropping variables that don't actually vary > > Hi, > > I am working with a large number of dummy variables and using collapse to > create derivative datasets that are the frequencies of 1's for each dummy > variable (a couple of hundred through foreach loops). I want to drop any of > the dummy variables that never had a 1 (so mean(dummy1)==0, or > max(dummy)==0) but it seems that drop only lets you use an if statement to > drop observations, but not an if statement to drop variables. > > My best guess is to use a list means to create a list of the variable names > that can be stored in a local and then fed into a drop command, but can't > seem to make that work either since I only want the list of variable names > that have a mean of 0. Or maybe transpose the dataset, drop then since the > variables are now observations, and transpose back? Another solution would > be save through StatTansfer and use it's drop constants feature, and then > bring the data back in, but there must be an easier way. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: RE: programatically dropping variables that don't actually vary***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: programatically dropping variables that don't actually vary***From:*"Earl, Jennifer Suzanne - (jenniferearl)" <jenniferearl@email.arizona.edu>

**st: RE: programatically dropping variables that don't actually vary***From:*"Sarah Edgington" <sedging@ucla.edu>

- Prev by Date:
**st: RE: Re: RE: Re: Skilmack across group** - Next by Date:
**Re: st: RE: programatically dropping variables that don't actually vary** - Previous by thread:
**st: RE: programatically dropping variables that don't actually vary** - Next by thread:
**Re: st: RE: programatically dropping variables that don't actually vary** - Index(es):