在 R 中查找以字符 position 开头的整个单词

Question

Str <- "I love chocolate pudding"
pos <- 8

I need to return the word that starts with the letter c at pos 8, which is chocolate. How can I do that?

Answer 1

You can use substring to get everything after 8th character. Then remove everything after space using gsub :

gsub(" .*", "", substring(Str, pos))

In case you need to check for the "c":

Str <- "I love dogs"

ifelse(
  substr(Str, pos, pos) == "c",
  gsub(" .*", "", substring(Str, pos)),
  ""
)

Answer 2

library(stringr)
str_extract(Str, "(?<=[\\w\\s]{7})\\bc\\w+\\b")
[1] "chocolate"

This solution uses str_extract and positive lookbehind (?<=[\\w\\s]{7}) , which can be glossed along these lines: "if you see seven characters consisting of alphanumeric characters ( \\w ) or white space ( \\s ) to the left, match the immediately next 'word' identified by its boundaries to either side ( \\b ) as well as the letter c occurring as the first letter of the word.

Alternatively, use sub and backreference:

sub(".{7}(\\bc\\w+\\b).*", "\\1", Str)
[1] "chocolate"

Answer 3

Using stringr and ignoring the 'starting with 'c' condition:

Str %>%
  str_sub(pos) %>%
  word(1)