[R] Data frames questions

[Douglas Bates]

On 9/23/06, X.H Chen <xchen_stat at hotmail.com> wrote:
> >1) Is there a way to build an empty data frame, containing nothing but the
> >data frame variable names?
>
> Yes, you can do it one way as followings:
>
> df1<-as.data.frame(matrix(nrow=2,ncol=2),row.names=c("R1","R2"))
>
> >2) Is there a way to reorder the variables in a data frame, e.g. When I go
> >to write out a data frame using write.table or write.matrix, I want the
> >output in a certain order...
>
> df2<-as.data.frame(matrix(1:4,nrow=2,ncol=2),row.names=c("R3","R4"))
> df2<-df2[c(2,1),]

I understood the question to be asking how to rearrange the variables
(i.e. columns of the data frame) instead of the rows (observations).
The same technique can be used but with the reordering vector on the
right hand side of the comma.  If you have named columns it may be
more accurate to use the names rather than the positions to get the
order you want.

> str(swiss)
`data.frame':	47 obs. of  6 variables:
 $ Fertility       : num  80.2 83.1 92.5 85.8 76.9 76.1 83.8 92.4 82.4 82.9 ...
 $ Agriculture     : num  17 45.1 39.7 36.5 43.5 35.3 70.2 67.8 53.3 45.2 ...
 $ Examination     : int  15 6 5 12 17 9 16 14 12 16 ...
 $ Education       : int  12 9 5 7 15 7 7 8 7 13 ...
 $ Catholic        : num   9.96 84.84 93.40 33.77  5.16 ...
 $ Infant.Mortality: num  22.2 22.2 20.2 20.3 20.6 26.6 23.6 24.9 21 24.4 ...
> head(swiss)
             Fertility Agriculture Examination Education Catholic
Infant.Mortality
Courtelary        80.2        17.0          15        12     9.96
       22.2
Delemont          83.1        45.1           6         9    84.84
       22.2
Franches-Mnt      92.5        39.7           5         5    93.40
       20.2
Moutier           85.8        36.5          12         7    33.77
       20.3
Neuveville        76.9        43.5          17        15     5.16
       20.6
Porrentruy        76.1        35.3           9         7    90.57
       26.6
> head(swiss[, c("Agriculture", "Education", "Examination", "Catholic")])
             Agriculture Education Examination Catholic
Courtelary          17.0        12          15     9.96
Delemont            45.1         9           6    84.84
Franches-Mnt        39.7         5           5    93.40
Moutier             36.5         7          12    33.77
Neuveville          43.5        15          17     5.16
Porrentruy          35.3         7           9    90.57

> >3) How to I "append" to the bottom of a dataframe?
>
> df2<-rbind(df2,c(5,6))
>
> Xiaohui Chen
>
> Dept. of Statistics
> UBC, Canada
>
>
>
>
> >From: Jonathan Greenberg <jgreenberg at arc.nasa.gov>
> >To: R-help <r-help at stat.math.ethz.ch>
> >Subject: [R] Data frames questions
> >Date: Sat, 23 Sep 2006 14:54:00 -0700
> >
> >Hi there, couple of questions on data frames:
> >
> >1) Is there a way to build an empty data frame, containing nothing but the
> >data frame variable names?
> >2) Is there a way to reorder the variables in a data frame, e.g. When I go
> >to write out a data frame using write.table or write.matrix, I want the
> >output in a certain order...
> >3) How to I "append" to the bottom of a dataframe?
> >
> >Thanks!
> >
> >--j
> >
> >--
> >Jonathan A. Greenberg, PhD
> >NRC Research Associate
> >NASA Ames Research Center
> >MS 242-4
> >Moffett Field, CA 94035-1000
> >Office: 650-604-5896
> >Cell: 415-794-5043
> >AIM: jgrn307
> >MSN: jgrn307 at hotmail.com
> >
> >______________________________________________
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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.
>
> ______________________________________________
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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.
>