[R] Erase content of dataframe in a single stroke

[Jim Lemon]

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
> > >
> > > ______________________________________________
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> > > and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Best regards,
> Luigi