[R] R 1.2.1 - read.table - factors problem or is it a data.frame problem

[Thomas Lumley]

On Wed, 31 Jan 2001 gordon.harrington at uni.edu wrote:
> However, the problem encountered is not one of setting factors but of unsetting
> them. The manual states that variables of mode or type character will become
> factors. My data input efforts showed no relationship between type and factor.
> With no evident reason, most character variables did not become factors while
> many real variables did. It is a bit disconcerting to get an output with
> thousands of floating point factor levels or error messages that one's data are
> of the wrong mode for any analysis whatsoever.
> 
> How does one unset mode assignment of factor and how does one avoid the problem
> of automatic misassignment with other datasets?

You can convert a factor to the correct numeric values with
   as.numeric(as.character(the.factor))

We don't have enough information to tell what happened in your case but in
my experience the most common reason for a numeric variable to read as a
factor has been misspecifying the missing value codes in the na.strings
argument. This argument lists the strings that should be converted to NAs;
any other strings will trigger a conversion to factor.

	-thomas

Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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