stri_split_fixed在R中的data.table中

Question

我有一个data.table DT如下.

DT <- structure(list(V1 = structure(1:3, .Label = c("S01", "S02", "S03" ), class = "factor"), V2 = structure(c(1L, 3L, 2L), .Label = c("Alan Hal << Guy John", "Bruce Dick Jean-Paul << Damien", "Jay << Barry Wally Bart"), class = "factor")), .Names = c("V1", "V2"), row.names = c(NA, -3L), class = "data.frame")
# DT
#    V1                             V2
# 1 S01           Alan Hal << Guy John
# 2 S02        Jay << Barry Wally Bart
# 3 S03 Bruce Dick Jean-Paul << Damien
setDT(DT)

我试图V2在"<<" 分割列,并在两个新列中获取输出.

我可以按照以下方式完成它 stringi

T <- as.data.frame(do.call(rbind,  stri_split_fixed(DT$V2, "<<", 2)))
setnames(T, old = colnames(T), new = c("V3", "V4"))
cbind(DT, T)
V1                             V2                    V3                V4
1: S01           Alan Hal << Guy John             Alan Hal           Guy John
2: S02        Jay << Barry Wally Bart                  Jay   Barry Wally Bart
3: S03 Bruce Dick Jean-Paul << Damien Bruce Dick Jean-Paul             Damien

但是我想通过:=运算符引用来做同样的事情.如何使用data.table执行此操作？

我对RHS部分有困难.

DT[, c("V1", "V2) := list()]

stri_split_fixed(DT$V2, "<<", 2) 给出一个3的列表,其中包含长度为2的字符向量.如何获得长度为3的字符向量的2列表？

Answer 1

你可以试试

setDT(DT)[, c('V3', 'V4'):=do.call(rbind.data.frame,
                    stri_split_fixed(V2, ' << ', 2))][]
#  V1                             V2                    V3                V4
#1: S01           Alan Hal << Guy John             Alan Hal           Guy John
#2: S02        Jay << Barry Wally Bart                  Jay   Barry Wally Bart
#3: S03 Bruce Dick Jean-Paul << Damien Bruce Dick Jean-Paul             Damien

或者你可以使用strsplit(来自@David Arenburg的评论)

 setDT(DT)[, c('V3', 'V4'):= do.call(rbind.data.frame,
                   strsplit(as.character(V2), " << "))] 

更有效的选择(由@Ananda Mahto建议)

cbind(DT, `colnames<-`(stri_split_fixed(DT$V2,
              " << ", simplify = TRUE), c("V3", "V4")))

另一种选择是使用cSplit由splitstackshape

library(splitstackshape)
cSplit(DT, 'V2', ' << ', stripWhite=FALSE, drop=FALSE)
#       V1                             V2                 V2_1             V2_2
#1: S01           Alan Hal << Guy John             Alan Hal         Guy John
#2: S02        Jay << Barry Wally Bart                  Jay Barry Wally Bart
#3: S03 Bruce Dick Jean-Paul << Damien Bruce Dick Jean-Paul           Damien

的更快的版本cSplit赋予类似性能stri_split是可Gist