[R] retaining formatting when converting a vector to amatrix/data.frame?

[Bert Gunter]

matrix() does not preserve class attributes, as it merely creates a matrix
of mode the mode of its argument (possibly after some coercion), which is
"numeric" for POSIXct, as you know. 

So why not just manually set the class attribute after creation of the
data.frame:

mydf <- data.frame(matrix(mydata,ncol=2))
for(i in seq(mydf))class(mydf[[i]]) <- class(mydata)

Cheers,

Bert Gunter
Genentech

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Thomas Pujol
Sent: Thursday, January 03, 2008 9:02 AM
To: r-help at stat.math.ethz.ch
Subject: [R] retaining formatting when converting a vector to
amatrix/data.frame?

Please see example code below.
   
  I have a vector ("mydata") of length 10.  "mydata" can have various
formats (e.g. numeric, text, POSIXct, etc)  I use the matrix and data.frame
functions to convert "mydata" to a dataframe ("mydf") of 2 columns and 5
rows.
   
  What is a "good" way to ensure that the format is retained when I create
the data.frame?
  Currently, data in the "POSIXct" format is converted to numeric.
   
  Also, for my edification, is there a "good" way to convert numeric values
such as these back to the original "POSIXct" format/values?
   
  Much thanks!
   
    #here I lose the "POSIXct" formatting

  mydata <- rep(Sys.time(), 10)
  str(mydata)
  mydf <- data.frame(matrix(data=mydata, nrow=5, ncol=2))
str(mydf)
   
    #here using only "matrix" I also lose the "POSIXct" formatting

    mydata <- rep(Sys.time(), 10)
  str(mydata)
  mydf <- matrix(data=mydata, nrow=5, ncol=2)
str(mydf)
   

    #this works as intended
  mydata <- rep(1:10)
  str(mydata)
  mydf <- data.frame(matrix(data=mydata, nrow=5, ncol=2))
str(mydf)


       
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