[R] how to check a R object's property

[Prof Brian Ripley]

On Tue, 14 Nov 2006, Weiwei Shi wrote:

> Hi,
> I am writing a generic function and need to check if an arg is a data
> frame or not.

?is.data.frame

> I could use is.null(dim(x)) to get what i want.

In which case you would fail. Arrays and many other objects have non-NULL 
dims.

> But i want to know if there is a
> function which can tell me whether it is a list, a numeric vector, a
> data frame, a factor and so on. Can R do that?

Yes.  ?typeof, ?class, ?str, ?inherits ... and please do study 'An 
Introduction to R' (belatedly).

You do seem to be asking almost daily for people to read the documentation 
for you.  Please try

install.packages("fortunes"); library(fortunes); fortune("WTFM")

-- 
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)
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