[R] Extract

[Val]

Hi All,

I want to extract new variables from a string and add it to the dataframe.
Sample data is csv file.

dat<-read.csv(text="Year, Sex,string
2002,F,15 xc Ab
2003,F,14
2004,M,18 xb 25 35 21
2005,M,13 25
2006,M,14 ac 256 AV 35
2007,F,11",header=TRUE)

The string column has  a maximum of five variables. Some rows have all
and others may not have all the five variables. If missing then  fill
it with NA,
Desired result is shown below,


Year,Sex,string, S1, S2, S3 S4,S5
2002,F,15 xc Ab, 15,xc,Ab, NA, NA
2003,F,14, 14,NA,NA,NA,NA
2004,M,18 xb 25 35 21,18, xb, 25, 35, 21
2005,M,13 25,13, 25,NA,NA,NA
2006,M,14 ac 256 AV 35, 14, ac, 256, AV, 35
2007,F,11, 11,NA,NA,NA,NA

Any help?
Thank you in advance.