[R] [EXT] Converting Date Time values

David K Stevens d@v|d@@teven@ @end|ng |rom u@u@edu
Mon Apr 26 21:27:22 CEST 2021

I use both routinely, depending on the need. 'ct' is great for 
representing date/time holistically (2021-04-26 13:21:27) and is numeric 
under the hood in seconds since the big bang (just kidding), kind of 
like julian seconds. 'lt' is a list of 7 elements that often require 
manipulation (e.g. lt$mon = month of the year starting with Jan = 0) but 
it's great for extracting values like day of the year, day of the week, 
etc. w/o having to do it yourself - saves a heap of error-fraught 
coding. One draw back is the handling of daylight savings shifts. In 
March, an hour gets lost (jumps from 0159 to 0300) and in October you 
get an hour twice, so if you're using code that requires 1 hour steps, 
you get hiccups twice/year, so that requires special handling. Don't 
overlook 'strptime' to convert non-standard dates (e.g. '4/26/21' isn't 
recognized by as.POSIXct but strptime can do the conversions for you.)

David Stevens

On 4/26/2021 12:26 PM, Jeff Reichman wrote:
> r-help
> Generally speaking is it better to convert date/time values to "POSIXlt" and
> "POSIXct" objects?
> Jeff Reichman
>          [[alternative HTML version deleted]]
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