[R] converting among modes

Thomas Lumley tlumley at u.washington.edu
Fri Jul 27 19:47:07 CEST 2001

On Fri, 27 Jul 2001, Martin Henry H. Stevens wrote:

> Windows 2000, R 1.3.0
> I have been given a data set (ASCII tab delimited) in which many variables
> that are supposed to be numeric actually contain characters. I would be
> happy to have those character entries disappear and become NA.
> When I use read.table and then attempt to convert these using as.numeric(),
> of course it doesn't work, and I get the ASCII? representation? maybe? When
> I use scan() and specify the data type (what=...), I get an error message
> saying that I have character data in the numeric variable.

If there are only a few different character strings causing problems you
can use the na.strings option of read.table().

Your data are actually read as *factors*, not as characters, and
as.numeric() gives the factor codes.  Converting factors to numeric is a
FAQ (7.13); use as.numeric(as.character(the.factor))


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

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