>>>>> Rich Shepard >>>>> on Wed, 10 Jun 2020 07:44:49 -0700 writes:
> On Wed, 10 Jun 2020, Jeff Newmiller wrote: >> Fix your format specification? ?strptime >>> I have been trying to convert European short dates >>> formatted as dd/mm/yy into the ISO 8601 but the function >>> as.Dates interprets them as American ones (mm/dd/yy), >>> thus I get: > Look at Hadley Wickham's 'tidyverse' collection as > described in R for Data Science. There are date, datetime, > and time functions that will do just what you want. > Rich I strongly disagree that automatic guessing of date format is a good idea: If you have dates such as 01/02/03, 10/11/12 , ... you cannot have a software (and also not a human) to *guess* for you what it means. You have to *know* or get that knowledge "exogenously", i.e., from context (say "meta data" if you want) that you as data analyst must have before you can reliably work with that data. There is a global standard (ISO) for dates, 2020-06-11, for today's; These have the huge advantage that alphabetical ordering is equivalent to time ordering ... and honestly I don't see why smart people (such as most? R users) do not all use these much more often, notably when it comes to data. But as long as most people in the world don't use that format and practically all default formats for dates (e.g. in spreadsheats and computer locales) do not use the ISO standard, but rather regional conventions, one must add meta data to have 100% garantee to use the correct format. Of course, you can often guess correctly with very high (subjective) probability, e.g., 11/23/99 is highly probably the 23rd of Nov, 1999.... and indeed if you have more than a few dates, it often helps to guess correctly. But there's no guarantee. No, I state that it is much better to ask from the data analyst to use their brains a little bit and enter the date format explicitly, than using software that does guess it for them correctly most of the time. How should they find out at all in the rare cases the automatic guess will be wrong ? Martin Maechler ETH Zurich and R Core team ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.