How to read data files containing time data by R?

For example, the data file test.dat is:

4188418000628;       1  ;    05-19-2002  ;    06-23-2002  ;     26.6;   3.71;   3.03;  0
4188418000628;       1  ;    05-19-2002  ;    07-15-2002  ;     28.1;   3.41;   2.79;  0
4188418000628;       1  ;    05-19-2002  ;    08-15-2002  ;     32.0;   3.43;   3.30;  0

The field is separated by ";" and the third and fourth columns are time data.

1. Read time data as characters.

   y<-read.table("test.dat", sep=";", as.is=T, strip.white=T)
   

   and we can get

   > y$V3
   [1] "05-19-2002" "05-19-2002" "05-19-2002"
   

   The argument strip.white is used only when sep has been specified, and allows the stripping of leading and trailing white space from `character' fields (`numeric' fields are always stripped). If strip.white=F, then we will get

   > y1<-read.table("test.dat", sep=";", as.is=T)
   > y1$V3
   [1] "    05-19-2002  " "    05-19-2002  " "    05-19-2002  "
   

   The default behavior of read.table is to convert character variables (which are not converted to logical, numeric or complex) to factors. When as.is=T, read.table will not convert character variables to factors.

    

2. Convert characters to a Julian date by using the function as.date in library(survival)

   library(survival)
   > a<-as.date(y$V3)
   > a
   [1] 19May2002 19May2002 19May2002
   > b
   [1] 23Jun2002 15Jul2002 15Aug2002
   > a[1]-b[1]
   [1] -35