R - import excel file

• the command read.xls("Path/to/data/data.xls") is part of the gdata package, so you have to install and load it
• str() shows the structure of the read data

Example:

library(ggplot2)
> x<-read.xls("c:\\R\\20110511daten.xls") # on Win
> x<-read.xls("~/R/20110511daten.xls") # on Unix
> str(x)
'data.frame':   7554 obs. of  20 variables:
$ sex : int  1 1 1 1 1 0 0 0 0 0 ...
$ date : Factor w/ 4312 levels "1966-Mar-01",..: 609 655 704 175 1920 2033 217 1899 977 ...
$ month : int  3 12 7 12 11 6 11 11 6 1 ...
$ year : int  2011 2008 2007 2007 2010 2008 2010 2007 2010 2010 ...
$ age : num  17.5 15.9 14 17.9 12.6 ...

everything is fine except the second variable: date is read as a factor not as date time; it has to be converted into a date.

• above you can see date is stored as "year-month-day"
• so all we have to do is the following:

library(ggplot2)> x$date<-as.Date(x$date, format="%Y-%b-%d")
> str(x)

'data.frame':   7554 obs. of  21 variables:
$ sex         : int  1 1 1 1 1 0 0 0 0 0 ...
$ date        :Class 'Date'  num [1:7554] 8629 8407 8572 7315 10342 ...
$ month       : int  3 12 7 12 11 6 11 11 6 1 ...
$ year        : int  2011 2008 2007 2007 2010 2008 2010 2007 2010 2010 ...

• now date has the class Date and if you run summary on it you get the right informations:
  > summary(x$date)
  

  Min.	1st Qu.	Median	Mean	3rd Qu.	Max.
  "1975-11-06"	"1995-08-13"	"1999-02-09"	"1998-12-31"	"2002-09-10"	"2008-02-17"

• further informations about the format argument you find here.