How to substring every element in vector of strings?

Question

I have the vector:

v <- c("godzilla", "jurassic", "googly")

I want the first 3 letters of every element in this vector. I would like to end up with:

# "god"   "jur"   "goo"

I have already tried using apply, but it didn't work. What should I do?

Topaz

See, @agstudy you got answer-bombed by Gavin :-) – Melbamelborn

Answer 1

One option is substring():

> substring(v, first = 1, last = 3)
[1] "god" "jur" "goo"

or also the R version, substr()

> substr(v, start = 1, stop = 3)
[1] "god" "jur" "goo"

Note the different names for the initial and last character you want.

As both of these functions are vectorised, there is no need for apply() and friends here.

Brachiate

How would one apply this to vectors within the rows of a data.frame? When I apply to a column by df2 <- df1 %>% mutate(y = substr(x, 0, 4)), I end up with the beginning of the concatenated list and the first characters of the first element of the list, e.g. "c("12" "c("24" "c("34". – Northampton

Answer 2

For the fun you can use a regular expression here :

sub('(^.{3}).*','\\1',v)
[1] "god" "jur" "goo"

Which is a another vectorized solution.

Album

Powerful, yet simple! +1 – Gca

Though this gets ugly if the length (3) is variable: sub(paste0('(^.{', len, '}).*'),'\\1',v) vs. substr(v, 1, len)... – Rattray

Answer 3

@Gavin Simpson's answer is the right way to go, but if you want to use apply() and friends here, you can try the following:

> sapply(strsplit(v, ""), function(x) paste0(x[1:3], collapse=""))
[1] "god" "jur" "goo"

Gca

gah. want to award points for curiosity but wouldn't want anyone to actually use this answer! – Janson

Yeah, this is just for fun. – Gca

This is the best answer to me, it helps you understand how functional programming works on R. – Homocercal

Answer 4

A stringr option is str_sub:

str_sub(v, 1, 3)
#[1] "god" "jur" "goo"

And str_sub_all for multiple substrings in each string:

str_sub_all(v, c(1, 2), c(3, 4))
# [[1]]
# [1] "god" "odz"
# 
# [[2]]
# [1] "jur" "ura"
# 
# [[3]]
# [1] "goo" "oog"

Shoeshine