[R] Regex exercise

[Marc Schwartz]

On Aug 20, 2010, at 4:16 PM, RICHARD M. HEIBERGER wrote:

> Bert,
> 
> we can save a lot of time by using paste and then only one call to eval and
> parse.
> 
>> x2 <- c("1",    "2:5",  "3:6", "4",    "8",    "5:7",  "10")
>> system.time(for (i in 1:100)  unlist(lapply(parse(text=x2),eval)))
>   user  system elapsed
>   0.06    0.00    0.03
>> system.time(for (i in 1:100)  eval(parse(text=paste("c(",paste(x2,
> collapse=","),")"))))
>   user  system elapsed
>   0.01    0.00    0.03
>> 
> 
> Rich


Building on Rich's approach:

> x
[1] "1   2 -5, 3- 6 4  8 5-7 10"


> eval(parse(text = paste("c(", paste(strsplit(gsub(" *- *", ":", x), split = " +|, +")[[1]], collapse = ","), ")")))
 [1]  1  2  3  4  5  3  4  5  6  4  8  5  6  7 10


The key inner part is:

> strsplit(gsub(" *- *", ":", x), split = " +|, +")[[1]]
[1] "1"   "2:5" "3:6" "4"   "8"   "5:7" "10" 


HTH,

Marc Schwartz