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

[Bill Dunlap]

The -grep(pattern,colnames) as a subscript is a bit dangerous.  If no
colname matches the pattern then all columns will be omitted (because -0 is
the same as 0, which means no column). !grepl(pattern,colnames) avoids this
problem.

> mydata <- data.frame(A=1:3,B=11:13)
> mydata[, -grep("^yr", colnames(mydata))]
data frame with 0 columns and 3 rows
> mydata[, !grepl("^yr", colnames(mydata))]
  A  B
1 1 11
2 2 12
3 3 13

-Bill

On Fri, Jan 13, 2023 at 11:07 PM Eric Berger <ericjberger using gmail.com> wrote:

> mydata[, -grep("^yr",colnames(mydata))]
>
> On Sat, Jan 14, 2023 at 8:57 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"...
> >
> > ______________________________________________
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> >
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>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
>

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