[R] NAs in chron objects

[Prof Brian Ripley]

On Fri, 18 May 2001, Markus Jantti wrote:

> Dear All:
>
> I am having some trouble with date variables when NAs are present. The
> following example illustrates (see below for output of version):

[...]

> dates() correctly produces the first NA's but becomes confused when
> strings with times start appearing. The below examples suggest the
> POSIXct class in the base package also has some trouble.

The trouble is your end: the error message means what it says,
and is explained the help page.  As the help page says,
specify the precise format, by in your case

as.POSIXct(strptime(minor.test[1:10], "%Y-%m-%d"))
 [1] "NA"             "NA"             "1988-02-08 GMT" "1988-02-08 GMT"
 [5] "NA"             "1987-11-23 GMT" "1988-09-03 BST" "1991-10-15 BST"
 [9] "1992-01-14 GMT" "1992-02-18 GMT"

Unless you specify the format, there is no way to distinguish invalid
entries from strings you mean to be NA, so the guessing algorithm give
up.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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