[R] using underscore character in column names

[Prof Brian D Ripley]

On Mon, 30 Aug 1999, Terry Westley wrote:

> Suppose you're reading data from a file in which the
> column names contain underscore characters.  Example:
> 
> ------ start of file -----
> pos_x   pos_y
>   1.0     0.0
>   2.0     1.0
> ------ end of file -------
> 
> Using read.table, I can read this file just fine:
> 
> > data <- read.table (file="data", head=T)
> > data
>   pos_x pos_y
> 1     1     0
> 2     2     1
> > 
> 
> However, I can't refer to pox_x because the _ character
> is an alternative to <- (assignment):
> 
> > data$pos_x
> Error: Object "x" not found
> 
> I could use data[1], but I'd prefer to use the column
> name.  Must I change all my column names to remove the
> underscore character or is there way to force R to
> recogize the whole column name?
> 
> Something like data${pos_x} or data$pos\_x  ???

data$"pos_x"

should work.  I don't know the exact R rules, but believe that you can make
quoted names work anywhere except as function argument names and in a few
odd places where deparsing is done. (Library sm has to be slightly
different from S to use its scripts without quotes, and they have _ in the
name.


-- 
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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