> rm(list=ls())
> library(stringr)
> x=data.frame(chr=c("abc.d","erf.f"),
+              num=c(123.2,345.7))
> 
> ###1
> m=strsplit(x$chr,"[.]")
> mm=do.call(cbind,m)
> mm
     [,1]  [,2] 
[1,] "abc" "erf"
[2,] "d"   "f"  
> 
> ###2
> m=strsplit(x$chr,".",fixed = T)
> mm=do.call(cbind,m)
> mm
     [,1]  [,2] 
[1,] "abc" "erf"
[2,] "d"   "f"  
> 
> ###3
> m=strsplit(x$chr,"\\.")
> mm=do.call(cbind,m)
> mm
     [,1]  [,2] 
[1,] "abc" "erf"
[2,] "d"   "f"  
> 
> ###4
> m=str_split(x$chr,"[.]",simplify = T)
> m
     [,1]  [,2]
[1,] "abc" "d" 
[2,] "erf" "f"