[R] string-to-number

[Mike Nielsen]

Wow.  New respect for parse/eval.

Do you think this is a special case of a more general principle?  I
suppose the cost is memory, but from time to time a speedup like this
would be very beneficial.

Any hints about how R programmers could recognize such cases would, I
am sure, be of value to the list in general.

Many thanks for your efforts, Marc!

Regards,

Mike

On 8/19/06, Marc Schwartz <MSchwartz at mn.rr.com> wrote:
> On Sat, 2006-08-19 at 13:30 +0100, Prof Brian Ripley wrote:
> > 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.
>
> I would say more than competitive:
>
>   repeated.measures.columns <- paste(1:100000, collapse = ",")
>
> > str(repeated.measures.columns)
>  chr
> "1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,4"| __truncated__
>
>
> > system.time(res1 <-
> as.numeric(unlist(strsplit(repeated.measures.columns, ","))))
> [1] 24.238  0.192 26.200  0.000  0.000
>
> > system.time(res2 <- as.numeric(strsplit(repeated.measures.columns,
> ",")[[1]]))
> [1] 24.313  0.196 26.471  0.000  0.000
>
> > system.time(res3 <- eval(parse(text=paste("c(",
> repeated.measures.columns, ")"))))
> [1] 0.328 0.004 0.395 0.000 0.000
>
>
> > str(res1)
>  num [1:100000] 1 2 3 4 5 6 7 8 9 10 ...
>
> > str(res2)
>  num [1:100000] 1 2 3 4 5 6 7 8 9 10 ...
>
> > str(res3)
>  num [1:100000] 1 2 3 4 5 6 7 8 9 10 ...
>
>
> > all(res1 == res2)
> [1] TRUE
>
> > all(res1 == res3)
> [1] TRUE
>
>
> Best regards,
>
> Marc
>
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-- 
Regards,

Mike Nielsen