how to remove all rows from a data.frame in r [duplicate]

Answer 1

If you really want to delete all rows:

> ddf <- ddf[0,]
> ddf
[1] vint1 vint2 vfac1 vfac2
<0 rows> (or 0-length row.names)    

If you mean by keeping the structure using placeholders:

> ddf[,]=matrix(ncol=ncol(ddf), rep(NA, prod(dim(ddf))))
> ddf
  vint1 vint2 vfac1 vfac2
1    NA    NA    NA    NA
2    NA    NA    NA    NA
3    NA    NA    NA    NA
4    NA    NA    NA    NA
5    NA    NA    NA    NA