[R] Quick Question about R

[Marc Schwartz]

On Wed, 2007-01-31 at 20:02 +0000, Ted.Harding at manchester.ac.uk wrote:
> On 31-Jan-07 Benilton Carvalho wrote:
> > suppressWarnings(a <- as.numeric(c(1, 2, pi, "a", 9, "z")))
> 
> Of course! Much better!
> Ted.

In the context of my prior reply:

# Bear in mind that the above vector is of class character, not mixed...
> str(c(1, 2, pi, "a", 9, "z"))
 chr [1:6] "1" "2" "3.14159265358979" "a" "9" "z"

> class(c(1, 2, pi, "a", 9, "z"))
[1] "character"


Thus:

> grep("[0-9\\.]", Vec, value = TRUE)
[1] "1"                "2"                "3.14159265358979"
[4] "9"               
 
> as.numeric(grep("[0-9\\.]", Vec, value = TRUE))
[1] 1.000000 2.000000 3.141593 9.000000

or:

> gsub("[A-Za-z]", "", Vec)
[1] "1"                "2"                "3.14159265358979"
[4] ""                 "9"                ""                
 
> as.numeric(gsub("[A-Za-z]", "", Vec))
[1] 1.000000 2.000000 3.141593       NA 9.000000       NA


The latter solution returns the NA's for non-convertible elements,
whereas the former, only the resultant numerics.

My preference is to be proactive in managing the data rather than
disabling warnings.  :-)

HTH,

Marc Schwartz