[R] Erase content of dataframe in a single stroke

[Jan van der Laan]

Or

testdf <- testdf[FALSE, ]

or

testdf <- testdf[numeric(0), ]

which seems to be slightly faster.

Best,
Jan


Op 27-9-2018 om 10:32 schreef PIKAL Petr:
> Hm
>
> I would use
>
>> testdf<-data.frame(A=c(1,2),B=c(2,3),C=c(3,4))
>> str(testdf)
> 'data.frame':   2 obs. of  3 variables:
>   $ A: num  1 2
>   $ B: num  2 3
>   $ C: num  3 4
>> testdf<-testdf[-(1:nrow(testdf)),]
>> str(testdf)
> 'data.frame':   0 obs. of  3 variables:
>   $ A: num
>   $ B: num
>   $ C: num
>
> Cheers
> Petr
>
>> -----Original Message-----
>> From: R-help <r-help-bounces using r-project.org> On Behalf Of Jim Lemon
>> Sent: Thursday, September 27, 2018 10:12 AM
>> To: Luigi Marongiu <marongiu.luigi using gmail.com>; r-help mailing list <r-help using r-
>> project.org>
>> Subject: Re: [R] Erase content of dataframe in a single stroke
>>
>> Ah, yes, try 'as.data.frame" on it.
>>
>> Jim
>>
>> On Thu, Sep 27, 2018 at 6:00 PM Luigi Marongiu <marongiu.luigi using gmail.com>
>> wrote:
>>> Thank you Jim,
>>> this requires the definition of an ad hoc function; strange that R
>>> does not have a function for this purpose...
>>> Anyway, it works but it changes the structure of the data. By
>>> redefining the dataframe as I did, I obtain:
>>>
>>>> df
>>> [1] A B C
>>> <0 rows> (or 0-length row.names)
>>>> str(df)
>>> 'data.frame': 0 obs. of  3 variables:
>>>   $ A: num
>>>   $ B: num
>>>   $ C: num
>>>
>>> When applying your function, I get:
>>>
>>>> df
>>> $A
>>> NULL
>>>
>>> $B
>>> NULL
>>>
>>> $C
>>> NULL
>>>
>>>> str(df)
>>> List of 3
>>>   $ A: NULL
>>>   $ B: NULL
>>>   $ C: NULL
>>>
>>> The dataframe has become a list. Would that affect downstream
>> applications?
>>> Thank you,
>>> Luigi
>>> On Thu, Sep 27, 2018 at 9:45 AM Jim Lemon <drjimlemon using gmail.com>
>> wrote:
>>>> Hi Luigi,
>>>> Maybe this:
>>>>
>>>> testdf<-data.frame(A=1,B=2,C=3)
>>>>> testdf
>>>>   A B C
>>>> 1 1 2 3
>>>> toNull<-function(x) return(NULL)
>>>> testdf<-sapply(testdf,toNull)
>>>>
>>>> Jim
>>>> On Thu, Sep 27, 2018 at 5:29 PM Luigi Marongiu
>> <marongiu.luigi using gmail.com> wrote:
>>>>> Dear all,
>>>>> I would like to erase the content of a dataframe -- but not the
>>>>> dataframe itself -- in a simple and fast way.
>>>>> At the moment I do that by re-defining the dataframe itself in this way:
>>>>>
>>>>>> df <- data.frame(A = numeric(),
>>>>> +                   B = numeric(),
>>>>> +                   C = character())
>>>>>> # assign
>>>>>> A <- 5
>>>>>> B <- 0.6
>>>>>> C <- 103
>>>>>> # load
>>>>>> R <- cbind(A, B, C)
>>>>>> df <- rbind(df, R)
>>>>>> df
>>>>>    A   B   C
>>>>> 1 5 0.6 103
>>>>>> # erase
>>>>>> df <- data.frame(A = numeric(),
>>>>> +                  B = numeric(),
>>>>> +                  C = character())
>>>>>> df
>>>>> [1] A B C
>>>>> <0 rows> (or 0-length row.names)
>>>>> Is there a way to erase the content of the dataframe in a simplier
>>>>> (acting on all the dataframe at once instead of naming each column
>>>>> individually) and nicer (with a specific erasure command instead
>>>>> of re-defyining the object itself) way?
>>>>>
>>>>> Thank you.
>>>>> --
>>>>> Best regards,
>>>>> Luigi
>>>>>
>>>>> ______________________________________________
>>>>> 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.
>>>
>>>
>>> --
>>> Best regards,
>>> Luigi
>> ______________________________________________
>> 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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