[R] rownames, colnames, and date and time

[Erich Neuwirth]

I noticed something surprising (in R 2.2.1 on WinXP)
According to the documentation, rownames and colnames are character vectors.
Assigning a vector of class POSIXct or POSIXlt as rownames or colnames
therefore is not strictly according to the rules.
In some cases, R performs a reasonable typecast, but in some other cases
where the same typecast also would be possible, it does not.

Assigning a vector of class POSIXct to the rownames or names of a
dataframe creates a reasonable string representation of the dates (and
possibly times).
Assigning such a vector to the rownames or colnames of a matrix produces
rownames or colnames consisting of the integer representation of the
date-time value.
Trying to assign a vector of class POSIXlt in all cases
(dataframes and matrices, rownames, colnames, names)
produces an error.

Demonstration code is given below.

This is somewhat inconsistent.
Perhaps a reasonable solution could be that the typecast
used for POSIXct and dataframes is used in all the other cases also.

Code:

mymat<-matrix(1:4,nrow=2,ncol=2)
mydf<-data.frame(mymat)
mydates<-as.POSIXct(c("2001-1-24","2005-12-25"))

rownames(mydf)<-mydates
names(mydf)<-mydates
rownames(mymat)<-mydates
colnames(mymat)<-mydates

print(deparse(mydates))
print(deparse(rownames(mydf)))
print(deparse(names(mydf)))
print(deparse(rownames(mymat)))
print(deparse(colnames(mymat)))

mydates1<-as.POSIXlt(mydates)

# the following lines will not work and
# produce errors

rownames(mydf)<-mydates1
names(mydf)<-mydates1
rownames(mymat)<-mydates1
colnames(mymat)<-mydates1


-- 
Erich Neuwirth
Institute for Scientific Computing and
Didactic Center for Computer Science
University of Vienna
phone: +43-1-4277-39464  fax: +43-1-4277-39459