[R] string-to-number

[Prof Brian Ripley]

On Sat, 19 Aug 2006, Marc Schwartz wrote:

> On Sat, 2006-08-19 at 07:58 -0400, Charles Annis, P.E. wrote:
> > Greetings, Amigos:
> > 
> > I have been trying without success to convert a character string,
> > > repeated.measures.columns
> > [1] "3,6,10"
> > 
> > into c(3,6,10) for subsequent use.
> > 
> > as.numeric(repeated.measures.columns) doesn't work (likely because of the
> > commas)
> > [1] NA
> > Warning message:
> > NAs introduced by coercion
> > 
> > I've tried many things including 
> > strsplit(repeated.measures.columns, split = ",")
> > 
> > which produces a list with only one element, viz:
> > [[1]]
> > [1] "3"  "6"  "10"
> > 
> > as.numeric() doesn't like that either.
> > 
> > Clearly: 1) I cannot be the first person to attempt this, and 2) I've made
> > this WAY harder than it is.
> > 
> > Would some kind soul please instruct me (and perhaps subsequent searchers)
> > how to convert the elements of a string into numbers?
> > 
> > Thank you.
> 
> One more step:
> 
> > as.numeric(unlist(strsplit(repeated.measures.columns, ",")))
> [1]  3  6 10
> 
> Use unlist() to take the output of strsplit() and convert it to a
> vector, before coercing to numeric.

Or, more simply, use [[1]] as in

as.numeric(strsplit(repeated.measures.columns, ",")[[1]])

Also,

eval(parse(text=paste("c(", repeated.measures.columns, ")")))

looks competitive, and is quite a bit more general (e.g. allows spaces, 
works with complex numbers), or you can use scan() from an anonymous file 
or a textConnection.

-- 
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 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595