On Jul 1, 2012, at 5:09 PM, David L Carlson wrote:
Yes it does have something to do with the representation of floating
point
numbers. Using cbind() forces the list to become a matrix and that
forces
all of the data to become character strings since one of the list
elements
is character:
set.seed(42)
listdat1<-list(
str(do.call("cbind", listdat1))
chr [1:10, 1:3] "21.3709584471467" "19.4353018286039" ...
Then you convert that to a data.frame. The default in data.frame()
is to
convert characters to factors so you get
str(data.frame(do.call("cbind",listdat1)))
'data.frame': 10 obs. of 3 variables:
$ X1: Factor w/ 10 levels "19.4353018286039",..: 8 1 5 7 6 2 9 3 10 4
$ X2: Factor w/ 2 levels "A","B": 1 2 1 2 1 2 1 2 1 2
$ X3: Factor w/ 5 levels "1","2","3","4",..: 1 2 3 4 5 1 2 3 4 5
Yes, arun. If the coding had proceeded otherwise a more natural and
expected result might have occurred:
> dat1<-do.call("data.frame",listdat1)
> colnames(dat1)<-c("Var1","Var2","Var3")
> dat1
Var1 Var2 Var3
1 21.14076 A 1
2 19.53277 B 2
3 19.59725 A 3
4 19.84262 B 4
5 19.93251 A 5
6 20.92242 B 1
7 19.22315 A 2
8 19.13742 B 3
9 18.82441 A 4
10 20.92661 B 5
Whoever taught you to use 'cbind' for construction of data.frames did
you a great disservice. It would seem much less problematic to have
simply done this in the first place:
dat1 <- data.frame(Var1=rnorm(10,20),Var2=rep(LETTERS[1:2],
5),var3=rep(1:5,2) )
--
David.
With dat2 you used data.frame() so the numeric fields were not
converted to
strings and then factors. Then you converted the dat1 factors back to
numeric. You would be fine with just
dat1 <- data.frame(listdat1)
colnames(dat1) <- paste0("Var", 1:3)
Or you can name the list elements and then convert
names(listdat1) <- paste0("Var", 1:3)
dat1 <- data.frame(listdat1)
----------------------------------------------
David L Carlson
Associate Professor of Anthropology
Texas A&M University
College Station, TX 77843-4352
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-bounces@r-
project.org] On Behalf Of arun
Sent: Sunday, July 01, 2012 12:56 PM
To: R help
Subject: [R] list to dataframe conversion-testing for identical
HI R help,
I was trying to get identical data frame from a list using two
methods.
#Suppose my list is:
listdat1<-list(rnorm(10,20),rep(LETTERS[1:2],5),rep(1:5,2))
#Creating dataframe using cbind
dat1<-data.frame(do.call("cbind",listdat1))
colnames(dat1)<-c("Var1","Var2","Var3")
#Second dataframe conversion
dat2<-
data.frame(Var1=listdat1[[1]],Var2=listdat1[[2]],Var3=listdat1[[3]])
#Structure is different in two datasets
>str(dat1)
'data.frame': 10 obs. of 3 variables:
$ Var1: Factor w/ 10 levels "18.6153321029756",..: 5 2 6 8 7 9 1 4 3
10
$ Var2: Factor w/ 2 levels "A","B": 1 2 1 2 1 2 1 2 1 2
$ Var3: Factor w/ 5 levels "1","2","3","4",..: 1 2 3 4 5 1 2 3 4 5
str(dat2)
'data.frame': 10 obs. of 3 variables:
$ Var1: num 20.3 19.2 20.5 20.9 20.5 ...
$ Var2: Factor w/ 2 levels "A","B": 1 2 1 2 1 2 1 2 1 2
$ Var3: int 1 2 3 4 5 1 2 3 4 5
#Converting structure of dat1 to match da2 structure
dat1<-within(dat1,{Var1<-as.numeric(as.character(Var1))
Var3<-as.integer(Var3)})
head(dat1)
Var1 Var2 Var3
1 20.27193 A 1
2 19.17586 B 2
3 20.53197 A 3
4 20.93615 B 4
5 20.53498 A 5
6 21.02044 B 1
head(dat2)
Var1 Var2 Var3
1 20.27193 A 1
2 19.17586 B 2
3 20.53197 A 3
4 20.93615 B 4
5 20.53498 A 5
6 21.02044 B 1
#New structure identical(str(dat1),str(dat2))
'data.frame': 10 obs. of 3 variables:
$ Var1: num 19.9 19 21.2 20.7 20.4 ...
$ Var2: Factor w/ 2 levels "A","B": 1 2 1 2 1 2 1 2 1 2
$ Var3: int 1 2 3 4 5 1 2 3 4 5
'data.frame': 10 obs. of 3 variables:
$ Var1: num 19.9 19 21.2 20.7 20.4 ...
$ Var2: Factor w/ 2 levels "A","B": 1 2 1 2 1 2 1 2 1 2
$ Var3: int 1 2 3 4 5 1 2 3 4 5
[1] TRUE
#structure is identical and dataframe looks to be same, but it is not
identical.
identical(dat1,dat2)
[1] FALSE
Is it something to do with the floating point?
Thanks,
A.K.
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______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
