[R] Removing variables from data frame with a wile card

[John Kane]

You rang sir?

library(tidyverse)
xx = 1:10
yr1 = yr2 = yr3 = rnorm(10)
dat1 <- data.frame(xx , yr1, yr2, y3)

dat1  %>%  select(!starts_with("yr"))

or for something a bit more exotic as I have been trying to learn a bit
about the "data.table package

library(data.table)

xx = 1:10
yr1 = yr2 = yr3 = rnorm(10)

dat2 <- data.table(xx , yr1, yr2, yr3)

dat2[, !names(dat2) %like% "yr", with=FALSE ]



On Sat, 14 Jan 2023 at 12:28, <avi.e.gross using gmail.com> wrote:

> Steven,
>
> Just want to add a few things to what people wrote.
>
> In base R, the methods mentioned will let you make a copy of your original
> DF that is missing the items you are selecting that match your pattern.
>
> That is fine.
>
> For some purposes, you want to keep the original data.frame and remove a
> column within it. You can do that in several ways but the simplest is
> something where you sat the column to NULL as in:
>
> mydata$NAME <- NULL
>
> using the mydata["NAME"] notation can do that for you by using a loop of
> unctional programming method that does that with all components of your
> grep.
>
> R does have optimizations that make this less useful as a partial copy of
> a data.frame retains common parts till things change.
>
> For those who like to use the tidyverse, it comes with lots of tools that
> let you select columns that start with or end with or contain some pattern
> and I find that way easier.
>
>
>
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Steven Yen
> Sent: Saturday, January 14, 2023 7:49 AM
> To: Andrew Simmons <akwsimmo using gmail.com>
> Cc: R-help Mailing List <r-help using r-project.org>
> Subject: Re: [R] Removing variables from data frame with a wile card
>
> Thanks to all. Very helpful.
>
> Steven from iPhone
>
> > On Jan 14, 2023, at 3:08 PM, Andrew Simmons <akwsimmo using gmail.com> wrote:
> >
> > You'll want to use grep() or grepl(). By default, grep() uses
> > extended regular expressions to find matches, but you can also use
> > perl regular expressions and globbing (after converting to a regular
> expression).
> > For example:
> >
> > grepl("^yr", colnames(mydata))
> >
> > will tell you which 'colnames' start with "yr". If you'd rather you
> > use globbing:
> >
> > grepl(glob2rx("yr*"), colnames(mydata))
> >
> > Then you might write something like this to remove the columns starting
> with yr:
> >
> > mydata <- mydata[, !grepl("^yr", colnames(mydata)), drop = FALSE]
> >
> >> On Sat, Jan 14, 2023 at 1:56 AM Steven T. Yen <styen using ntu.edu.tw> wrote:
> >>
> >> I have a data frame containing variables "yr3",...,"yr28".
> >>
> >> How do I remove them with a wild card----something similar to "del yr*"
> >> in Windows/doc? Thank you.
> >>
> >>> colnames(mydata)
> >>   [1] "year"       "weight"     "confeduc"   "confothr" "college"
> >>   [6] ...
> >>  [41] "yr3"        "yr4"        "yr5"        "yr6" "yr7"
> >>  [46] "yr8"        "yr9"        "yr10"       "yr11" "yr12"
> >>  [51] "yr13"       "yr14"       "yr15"       "yr16" "yr17"
> >>  [56] "yr18"       "yr19"       "yr20"       "yr21" "yr22"
> >>  [61] "yr23"       "yr24"       "yr25"       "yr26" "yr27"
> >>  [66] "yr28"...
> >>
> >> ______________________________________________
> >> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> >> http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
>
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>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
John Kane
Kingston ON Canada

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