[R] Extracting a numeric prefix from a string

[(Ted Harding)]

On 31-Jan-05 R user wrote:
> You could use something like
> 
> y <- gsub('([0-9]+(.[0-9]+)?)?.*','\\1',x)
> as.numeric(y)
> 
> But maybe there's a much nicer way.
> 
> Jonne.

I doubt it -- full marks for neat regexp footwork!

To comply fully with Mike's request, I'd wrap it in sort():

  sort(as.numeric(y),na.last=TRUE)
  [1] 2.40 2.40 3.00 3.00 4.20 5.67 6.00 6.00   NA

or even

  unique(sort(as.numeric(y),na.last=TRUE))
  [1] 2.40 3.00 4.20 5.67 6.00   NA

Cheers,
Ted.

> On Mon, 2005-01-31 at 08:51 +0000, Mike White wrote:
>> Hi
>> Does anyone know if there is a function similar to as.numeric that
>> will
>> extract a numeric prefix from a string as in the following examples?
>> 
>> x<-c(3, "abc", 5.67, "2.4a", "6a", "6b", "2.4.a", 3, "4.2a")
>> df.x<-data.frame(Code=x)
>> x.str<-levels(df.x[,1])
>> # required function  result
>> 2.40 3.00 4.20 5.67 6.00 NA
>> 
>> Thanks
>> Mike White
>> 
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> R user <R-user at zutt.org>
> 
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Date: 31-Jan-05                                       Time: 16:09:49
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