[Rd] RFC: type conversion in read.table

[Prof Brian Ripley]

On Sat, 1 Sep 2001, Kurt Hornik wrote:

> >>>>> Prof Brian D Ripley writes:
>
> > On Fri, 31 Aug 2001, Kurt Hornik wrote:
> >> > Prof Brian Ripley wrote:
> >> >>
> >> >> Currently read.table is rather limited in its type conversion.
> >> >> The algorithm is
> >> >>
> >> >> 0) Read as character
> >> >> 1) Try to convert to numeric. If that works, quit
> >> >> 2) Convert to factor unless !as.is.
> >> >>
> >> >> I am thinking about adding more flexibility and more classes by the
> >> >> following two changes.
> >> >>
> >> >> A) Anticipating the arrival of classes for all R objects, add an
> >> >> argument say `colClasses' that allows the user to specify the desired
> >> >> class for every column.  This could default to "auto", or NA if people
> >> >> think "auto" might be a relevant class name one day.
> >> >>
> >> >> The effect would be equivalent to running
> >> >>
> >> >> data[[i]] <- as(data[[i]], colClasses[i])
> >> >>
> >> >> instead of
> >> >>
> >> >> data[[i]] <- type.convert(data[[i]], as.is = as.is[i], dec = dec)
> >> >>
> >> >> except that standard classes such as "numeric", "factor", "logical",
> >> >> "character" would be dispatched directly, and argument "dec" would be
> >> >> consulted where appropriate.
> >> >>
> >> >> colClasses = "character" would suppress all conversions, which cannot
> >> >> currently be done.
> >>
> >> Just a small remark.  I would prefer `NA' to "auto" (or "unknown").  May
> >> be too late to change this now :-)
>
> > Anything can be changed up to 1.4.0 release.  In particular, the
> > present code will have to be changed unless as() is in base by then.
>
> Ok.  Can I formally propose to use NA then?  (I guess this convention
> could be useful in similar situations as well.)

Already done.

[...]

-- 
Brian D. Ripley,                  ripley@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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