Hi Luigi,
Actually I doubt that the original problem you try to solve requires the
initialization of an empty data.frame with a particular structure.
However, if you think you really need this step, I would write a
function for it and also consider edge cases.
getSkeleton <- function(x, drop_levels = FALSE) {
out <- x[numeric(0L), , drop = FALSE]
if (isTRUE(drop_levels)) out <- droplevels(out)
out
}
Note that it retains or drops factor levels depending on 'drop_levels'.
It only matters if you have factors in your data.frame.
'drop = FALSE' is required to guard against silent conversion to a
vector if 'x' has only one column.
Regards,
Denes
On 09/27/2018 11:11 AM, Jan van der Laan wrote:
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-boun...@r-project.org> On Behalf Of Jim Lemon
Sent: Thursday, September 27, 2018 10:12 AM
To: Luigi Marongiu <marongiu.lu...@gmail.com>; r-help mailing list
<r-help@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.lu...@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 <drjimle...@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.lu...@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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--
Best regards,
Luigi
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PLEASE do read the posting guide
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