R tips: Use read.table instead of strsplit to split a text column into multiple columns

May 29, 2009
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Someone on the R-help mailing list had a data frame with a column containing IP addresses in quad-dot format (e.g. 1.10.100.200). He wanted to sort by this column and I proposed a solution involving strsplit. But Peter Dalgaard comes up with a much nicer method using read.table on a textConnection object:

> a <- data.frame(cbind(color=c("yellow","red","blue","red"),
                        status=c("no","yes","yes","no"),
                        ip=c("162.131.58.26","2.131.58.16","2.2.58.10","162.131.58.17")))
> con <- textConnection(as.character(a$ip))
> o <- do.call(order,read.table(con, sep="."))
> close(con)
> a[o,]
   color status            ip
3   blue    yes     2.2.58.10
2    red    yes   2.131.58.16
4    red     no 162.131.58.17
1 yellow     no 162.131.58.26

That is very, very neat! Thank you Peter.

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