apply strsplit rowwise | 易学教程

问题

Im trying to split a string on "." and create additional columns with the two strings before and after ".".

tes<-c("1.abc","2.di","3.lik")
dat<-c(5,3,2)
h<-data.frame(tes,dat)
h$num<-substr(h$tes,1,1)

h$prim<-unlist(strsplit(as.character(h$tes),"\\."))[2]
h$prim<-sapply(h$tes,unlist(strsplit(as.character(h$tes),"\\."))[2])

I´d like h$prim to contain "abc","di","lik"..However I´m not able to figure it out. I guess strsplit is not vectorized, but then I thought the sapply version should have worked. However I assume it should be easy:-)

Regards, //M

回答1:

This should do the trick

R> sapply(strsplit(as.character(h$tes), "\\."), "[[", 2)
[1] "abc" "di"  "lik"

回答2:

With the stringr package it's even easier:

library(stringr)
str_split_fixed(h$tes, fixed("."), 2)[, 2]

回答3:

This is the same as rcs' answer, but may be easier to understand:

> sapply(strsplit(as.character(h$tes), "\\."), function(x) x[[2]])
[1] "abc" "di"  "lik"

回答4:

This question appears several time on StackOverflow.

In exact form as yours:

Selecting first element of strsplit
Selecting second element separate by space
Selecting second element separate by dot I recommend this question to see in how many ways it could be achieved.

Some similar question in this topic:

Split without separator
First part as in your question but was change to more complex case

And if you care about speed then you should consider tip from John answer about fixed parameter to strsplit.

回答5:

Alternatively, you can save yourself the work of pulling out the 2nd element if you add both columns at the same time:

tes <- c("1.abc","2.di","3.lik")
dat <- c(5,3,2)
h <- data.frame(tes, dat, stringsAsFactors=FALSE)
values <- unlist(strsplit(h$tes, ".", fixed=TRUE))
h <- cbind(h, matrix(values, byrow=TRUE, ncol=2,
                     dimnames=list(NULL, c("num", "prim"))))

来源：https://stackoverflow.com/questions/3703803/apply-strsplit-rowwise

标签

strsplit