First entry from string split

Question

I\'ve got a column people$food that has entries like chocolate or apple-orange-strawberry.

I want to split people$food

Answer 1

dplyr/magrittr approach:

library(magrittr)
library(dplyr)

word = c('apple-orange-strawberry', 'chocolate')

strsplit(word, "-") %>% sapply(extract2, 1)
# [1] "apple"     "chocolate"

Answer 2

I would use sub() instead. Since you want the first "word" before the split, we can simply remove everything after the first - and that's what we're left with.

sub("-.*", "", people$food)

Here's an example -

x <- c("apple", "banana-raspberry-cherry", "orange-berry", "tomato-apple")
sub("-.*", "", x)
# [1] "apple"  "banana" "orange" "tomato"

Otherwise, if you want to use strsplit() you can round up the first elements with vapply()

vapply(strsplit(x, "-", fixed = TRUE), "[", "", 1)
# [1] "apple"  "banana" "orange" "tomato"

Answer 3

I would suggest using head rather than [ in R.

word <- c('apple-orange-strawberry','chocolate')
sapply(strsplit(word, "-"), head, 1)
# [1] "apple"     "chocolate"

Answer 4

For example

word <- 'apple-orange-strawberry'

strsplit(word, "-")[[1]][1]
[1] "apple"

or, equivalently

unlist(strsplit(word, "-"))[1].

Essentially the idea is that split gives a list as a result, whose elements have to be accessed either by slicing (the former case) or by unlisting (the latter).

If you want to apply the method to an entire column:

first.word <- function(my.string){
    unlist(strsplit(my.string, "-"))[1]
}

words <- c('apple-orange-strawberry', 'orange-juice')

R: sapply(words, first.word)
apple-orange-strawberry            orange-juice 
                "apple"                "orange"

Answer 5

If you need to extract the first (or nth) entry from each split, use:

word <- c('apple-orange-strawberry','chocolate')

sapply(strsplit(word,"-"), `[`, 1)
#[1] "apple"     "chocolate"

Or faster and more explictly:

vapply(strsplit(word,"-"), `[`, 1, FUN.VALUE=character(1))
#[1] "apple"     "chocolate"

Both bits of code will cope well with selecting whichever value in the split list, and will deal with cases that are outside the range:

vapply(strsplit(word,"-"), `[`, 2, FUN.VALUE=character(1))
#[1] "orange" NA