R help - Jan 2023 - Removing variables from data frame with a wile card

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"...

mydata[, -grep("^yr",colnames(mydata))]

On Sat, Jan 14, 2023 at 8:57 AM Steven T. Yen <styen at 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 at 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.
>
	[[alternative HTML version deleted]]

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 at 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 at 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.