[R] data.frame() versus as.data.frame() applied to a matrix.

[William Dunlap]

I think of the methods of as.data.frame as a helper functions for
data.frame and don't usually call as.data.frame directly.  data.frame()
will call as.data.frame for each of its arguments and then put together the
the results into one big data.frame.

> for(method in
c("as.data.frame.list","as.data.frame.character","as.data.frame.integer","as.data.frame.numeric","as.data.frame.matrix"))
trace(method, quote(str(x)))
Tracing function "as.data.frame.list" in package "base"
Tracing function "as.data.frame.character" in package "base"
Tracing function "as.data.frame.integer" in package "base"
Tracing function "as.data.frame.numeric" in package "base"
Tracing function "as.data.frame.matrix" in package "base"
> d <-
data.frame(Mat=cbind(m1=11:12,M2=13:14),Num=c(15.5,16.6),Int=17:18,List=list(L1=19:20,L2=c(20.2,21.2)))
Tracing as.data.frame.matrix(x[[i]], optional = TRUE) on entry
 int [1:2, 1:2] 11 12 13 14
 - attr(*, "dimnames")=List of 2
  ..$ : NULL
  ..$ : chr [1:2] "m1" "M2"
Tracing as.data.frame.numeric(x[[i]], optional = TRUE) on entry
 num [1:2] 15.5 16.6
Tracing as.data.frame.integer(x[[i]], optional = TRUE) on entry
 int [1:2] 17 18
Tracing as.data.frame.list(x[[i]], optional = TRUE, stringsAsFactors =
stringsAsFactors) on entry
List of 2
 $ L1: int [1:2] 19 20
 $ L2: num [1:2] 20.2 21.2
Tracing as.data.frame.integer(x[[i]], optional = TRUE) on entry
 int [1:2] 19 20
Tracing as.data.frame.numeric(x[[i]], optional = TRUE) on entry
 num [1:2] 20.2 21.2

If I recall correctly, that is how S did things and Splus tried to use
something like as.data.frameAux for the name of the helper function to
avoid some of the frustration you describe.

Bill Dunlap
TIBCO Software
wdunlap tibco.com


On Tue, Feb 5, 2019 at 2:22 PM Rolf Turner <r.turner using auckland.ac.nz> wrote:

>
> Consider the following:
>
> set.seed(42)
> X <- matrix(runif(40),10,4)
> colnames(X) <- c("a","b","a:x","b:x") # Imitating the output
>                                        # of model.matrix().
> D1 <- as.data.frame(X)
> D2 <- data.frame(X)
> names(D1)
> [1] "a"   "b"   "a:x" "b:x"
> names(D2)
> [1] "a"   "b"   "a.x" "b.x"
>
> The names of D2 are syntactically valid; those of D1 are not.
>
> Why should I have expected this phenomenon? :-)
>
> The as.data.frame() syntax seems to me much more natural for converting
> a matrix to a data frame, yet it doesn't get it quite right, sometimes,
> in respect of the names.
>
> Is there some reason that as.data.frame() does not apply make.names()?
> Or was this just an oversight?
>
> cheers,
>
> Rolf Turner
>
> --
> Honorary Research Fellow
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
>
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