[R] seq(2,5,-2) not an error but NULL
andy_liaw at merck.com
Mon Mar 27 14:26:42 CEST 2006
You should be able to do it yourself; e.g.,
my.seq <- function(...) if((to - from) * by < 0) NULL else seq(...)
and use that instead when you want that behavior.
From: Christian Hoffmann
> This may belong more to r-develop, but general discussion may
> be useful
> (for the how many-th time ?)
> both result in
> Error in seq.default(2, 5, -2) : wrong sign in 'by' argument
> But often, if not always, mathematicians and programmers want a
> behaviour e.g. in for loops, where this statement results in an empty
> statement, that is
> for (ii in seq(2,5,-2)) print(ii)
> were equivalent to
> for (ii in NULL) print(ii).
> The relevant part in seq.default is now
> if (n < 0)
> stop("wrong sign in 'by' argument")
> but could be changed by option to
> I think there should be an option to seq requiring this
> behaviour, or a
> specific function, may be even a special operator, e.g. %;%:
> 3;5 resulting in NULL.
> What do you think?
> Dr. Christian W. Hoffmann,
> Swiss Federal Research Institute WSL
> Mathematics + Statistical Computing
> Zuercherstrasse 111
> CH-8903 Birmensdorf, Switzerland
> Tel +41-44-7392-277 (office) -111(exchange)
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> christian.hoffmann at wsl.ch http://www.wsl.ch/staff/christian.hoffmann
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