如何通过字数优雅地将字符串分成两半？

Question

我需要按字数将字符串分成两半（当单词数为奇数时，中间的单词应该出现在左侧和右侧）。我还需要知道每个字符串来自哪一侧。

my_question <- data.frame(string_id = c(001, 002, 003), 
    string = (c("how do I split", "how do I split this", "how do I split this string")))

my_answer <- data.frame(string_id = c(001, 002, 003, 001, 002, 003), 
    string = (c("how do", "how do I", "how do I", "I split", "I split this", "split this string")), 
     side = c("R", "R", "R", "L", "L", "L"))

我更喜欢使用 stringr/tidyverse/hadleyverse。

Answer 1

我们可以编写一些辅助函数来简化这个过程

library(tidyverse)
word_split <- function(x, side="left", sep=" ") {
  words <- strsplit(as.character(x), sep)
  nwords <- lengths(words)
  if(side=="left") {
    start <- 1
    end <- ceiling(nwords/2)
  } else if (side=="right") {
    start <- ceiling((nwords+1)/2)
    end <- nwords
  }
  cw <- function(words, start, stop) paste(words[start:stop], collapse=sep)
  pmap_chr(list(words, start, end), cw)
}
left_words <- function(..., side) word_split(..., side="left")
right_words <- function(..., side) word_split(..., side="right")

那我们可以用更传统的管道链来分享你想要的结果

my_question %>% mutate(L=left_words(string),
                       R=right_words(string)) %>%
  select(-string) %>% 
  gather(side, string, L:R)

导致

  string_id side            string
1         1    L            how do
2         2    L          how do I
3         3    L          how do I
4         1    R           I split
5         2    R      I split this
6         3    R split this string