How to split a sentence in two halves in R - r

Question

I have a vector of string, and I want each string to be cut roughly in half, at the nearest space.
For exemple, with the following data :
test <- data.frame(init = c("qsdf mqsldkfop mqsdfmlk lksdfp pqpdfm mqsdfmj mlk",
"qsdf",
"mp mlksdfm mkmlklkjjjjjjjjjjjjjjjjjjjjjjklmmjlkjll",
"qsddddddddddddddddddddddddddddddd",
"qsdfmlk mlk mkljlmkjlmkjml lmj mjjmjmjm lkj"), stringsAsFactors = FALSE)
I want to get something like this :
first sec
1 qsdf mqsldkfop mqsdfmlk lksdfp pqpdfm mqsdfmj mlk
2 qsdf
3 mp mlksdfm mkmlklkjjjjjjjjjjjjjjjjjjjjjjklmmjlkjll
4 qsddddddddddddddddddddddddddddddd
5 lmj mjjmjmjm lkj lmj mjjmjmjm lkj
Any solution that does not cut in halves but "so that the first part isn't longer than X character" would be also great.

Answer 1

First, we split the strings by spaces.
a <- strsplit(test$init, " ")
Then we find the last element of each vector for which the cumulative sum of characters is lower than half the sum of all characters in the vector:
b <- lapply(a, function(x) which.max(cumsum(cumsum(nchar(x)) <= sum(nchar(x))/2)))
Afterwards we combine the two halfs, substituting NA if the vector was of length 1 (only one word).
combined <- Map(function(x, y){
if(y == 1){
return(c(x, NA))
}else{
return(c(paste(x[1:y], collapse = " "), paste(x[(y+1):length(x)], collapse = " ")))
}
}, a, b)
Finally, we rbind the combined strings and change the column names.
newdf <- do.call(rbind.data.frame, combined)
names(newdf) <- c("first", "second")
Result:
> newdf
first second
1 qsdf mqsldkfop mqsdfmlk lksdfp pqpdfm mqsdfmj mlk
2 qsdf <NA>
3 mp mlksdfm mkmlklkjjjjjjjjjjjjjjjjjjjjjjklmmjlkjll
4 qsddddddddddddddddddddddddddddddd <NA>
5 qsdfmlk mlk mkljlmkjlmkjml lmj mjjmjmjm lkj

Answer 2

You can use the function nbreak from the package that I wrote:
devtools::install_github("igorkf/breaker")
library(tidyverse)
test <- data.frame(init = c("Phrase with four words", "That phrase has five words"), stringsAsFactors = F)
#This counts the numbers of words of each row:
nwords = str_count(test$init, " ") + 1
#This is the position where break the line for each row:
break_here = ifelse(nwords %% 2 == 0, nwords/2, round(nwords/2) + 1)
test
# init
# 1 Phrase with four words
# 2 That phrase has five words
#the map2_chr is applying a function with two arguments,
#the string is "init" and the n is "break_here":
test %>%
mutate(init = map2_chr(init, break_here, ~breaker::nbreak(string = .x, n = .y, loop = F))) %>%
separate(init, c("first", "second"), sep = "\n")
# first second
# 1 Phrase with four words
# 2 That phrase has five words