R - converting integers or strings into date format

• as.Date(x,format="")
• dates are given in a lot of different formats, e.g.
  
  • "2011-03-14"
  • "2011-Mar-14"
  • "11-March-14"
• if you want to convert them you have to tell R which format your dates have, here some examples:

> as.Date("2011-03-14",format="%Y-%m-%d")

[1] "2011-03-14"

> as.Date("2011/03/14", format="%Y/%m/%d")

[1] "2011-03-14"

> as.Date("14.3.2011", format="%d.%m.%Y")

[1] "2011-03-14"

> as.Date("2011-Sep-14", format="%Y-%b-%d")

[1] "2011-09-14"

> as.Date("2011-september-14", format="%Y-%B-%d")

[1] "2011-09-14"

> as.Date("14. November 1999", format="%d. %B %Y")

[1] "1999-11-14"

• here are the codes:
  

  Code	Value
  %d	Day of the month (decimal number)
  %m	Month (decimal number)
  %b	Month (abbreviated)
  %B	Month (full name)
  %y	Year (2 digits)
  %Y	Year (4 digits)

• if the date is given as integer you have to specify the origin - R counts in days. e.g. in SPSS  a date is stored in seconds, the origin is 1582-10-14. So you have divide by 86400 (=24*60*60); for example if 1000000 is given the command is:

> as.Date(1000000/86400, origin="1582-10-14")

[1] "1582-10-25"  the origin in Excel: 1900-01-01; SAS: 1960-01-01; R: 1970-01-01