> -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On > Behalf Of Joshua Wiley > Sent: Thursday, March 25, 2010 1:48 PM > To: anna > Cc: r-help@r-project.org > Subject: Re: [R] Convert number to Date > > Dear Anna, > > Rolf's explanation not withstanding, it has to do with differences in > how R and Excel treat dates. If you use > > as.Date(40182, origin="1899-12-30") > > you will get the same date as Excel. You can look at: > > http://office.microsoft.com/training/training.aspx?AssetID=RC102786151033&CTT= > 6&Origin=RP102786121033 > > For an official guide on how Excel dates are calculated. Apparently, > Excel's calendar starts on 1 January 1900. Why one has to use an > origin of 30 December 1899 in R...well, I suspect that gets back to > Rolf's explanation. > > > HTH, > > Josh > <<<snip>>>
The reason one must use 1899-12-30, as the origin, is 1. Excel treats 1900-01-01 as day 1, but as.Date() teats the origin as day 0. 2. According to Wikipedia, Excel copied the Lotus 1-2-3 error of making 1900 a leap year (an extra day) That accounts for the two day difference. Hope this is helpful, Dan Daniel J. Nordlund Washington State Department of Social and Health Services Planning, Performance, and Accountability Research and Data Analysis Division Olympia, WA 98504-5204 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
