[R] using underscore character in column names

[Thomas Lumley]

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  ???

Well, data$"pos_x" should work, but it would really be better to change
the name to pos.x instead.  I don't think work-arounds like this will be
available for all R commands. For example, I don't think you can trick
model formulas into accepting names with underscores in.


Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle



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