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

[Steven T. Yen]

In the line suggested by Andrew Simmons,

mydata <- mydata[, !grepl("^yr", colnames(mydata)), drop = FALSE]

what does drop=FALSE do? Thanks.

On 1/14/2023 8:48 PM, Steven Yen wrote:
> 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"...
>>>
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