pattern matching with sub(), unable to catch and replace first occurrence - r

Question

The followings are the results I expect
> title = "La La Land (2016/I)"
[1]"(2016" #result
> title = "_The African Americans: Many Rivers to Cross with Henry Louis Gates, Jr._ (2013) _The Black Atlantic (1500-1800) (#1.1)_"
[1]"(2013" #result
> title = "dfajfj(2015)asdfjuwer f(2017)fa.erewr6"
[1]"(2015" #result
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The followings are what I got by applying codesub(pattern=".*(\\(\\d{4}.*\\)).*", title, replacement="\\1")
> title = "_The African Americans: Many Rivers to Cross with Henry Louis Gates, Jr._ (2013) _The Black Atlantic (1500-1800) (#1.1)_"
> sub(pattern=".*(\\(\\d{4}.*\\)).*", title, replacement="\\1")
[1] "(1500-1800) (#1.1)" #result. However, I expected it to be "(2013)"
> title = "La La Land (2016/I)"
> sub(pattern=".*(\\(\\d{4}.*\\)).*", title, replacement="\\1")
[1] "(2016/I)" #result as I expect
> title = "dfajfj(2015)asdfjuwer f(2017)fa.erewr6"
> sub(pattern=".*(\\(\\d{4}.*\\)).*", title, replacement="\\1")
[1]"(2017)" # result. However, I expect it to be "（2015)"
The followings are what I GOT by applying codesub(pattern=".*(\\(\\d{4}\\)).*", title, replacement="\\1")
> title = "La La Land (2016/I)"
> sub(pattern=".*(\\(\\d{4}\\)).*", title, replacement="\\1")
[1] "La La Land (2016/I)" #result. However, I expect it to be "(2016)"
> title = "dfajfj(2015)asdfjuwer f(2017)fa.erewr6"
> sub(pattern=".*(\\(\\d{4}\\)).*", title, replacement="\\1")
[1] "(2017)" #result. However, I expect it to be "(2015)"
> title = "_The African Americans: Many Rivers to Cross with Henry Louis Gates, Jr._ (2013) _The Black Atlantic (1500-1800) (#1.1)_"
> sub(pattern=".*(\\(\\d{4}\\)).*", title, replacement="\\1")
[1] "(2013)" #result as I expect
I checked the description of sub, it says "sub performs replacement of the first match. In this case, the first match should be (2013).
In a word, I try to write a sub()command to return the first occurrence of a year in a string.
I guess there is something wrong with my code but couldn't find it, appreciate if anyone could help me.
==================================================================
In fact, my ultimate goal is to extract the year of all movies. However, I don't know how to do it in one step. Therefore, I decide to first find the year in (dddd format, then use code sub(pattern="\\((\\d{4}).*", a, replacement="\\1") to find the pure number of the year.
for example:
> a= "(2015"
> sub(pattern="\\((\\d{4}).*", a, replacement="\\1")
[1] "2015"
> a= "(2015)"
> sub(pattern="\\((\\d{4}).*", a, replacement="\\1")
[1] "2015"
=================updated 05/29/2017 22:51PM=======================
the str_extract in akrun's answer works well with my dataset.
However, the sub() doesn't work for all data. The following are what I did. However, my code doesn't work with all 500 records. I would really appreciate if anyone could point out the mistakes on my codes. I really cannot figure it out myself. Thank you very much.
> t1
[1] "Man Who Fell to Earth (Remix) (2010) (TV)"
> t2
[1] "Manual pr\u0087ctico del amigo imaginario (abreviado) (2008)"
> title = c(t1,t2)
> x=gsub(pattern=".*(\\(\\d{4}.*\\)).*", title, replacement="\\1")
> x
[1] "(2010) (TV)" "(2008)"
> sub(pattern="\\((.*)\\).*", x, replacement="\\1")
[1] "2010) (TV" "2008"
However, my goal is to get 2010 and 2008. My code works with t2 but fails with t1

Answer 1

We can match 0 or more characters that are not a ( ([^(]*) from the start (^) of the string, followed by a ( and four digits (\\([0-9]{4}) which we capture as a group ((...)) followed by other characters (.*) and replace with the backreference (\\1) of the captured group
sub("^[^(]*(\\([0-9]{4}).*", "\\1", title)
#[1] "(2016" "(2013" "(2015"
If we need to remove the (, then capture only the numbers that follows the \\( as a group
sub("^[^(]*\\(([0-9]{4}).*", "\\1", title)
#[1] "2016" "2013" "2015"
Or with str_extract, we use a regex lookaround to extract the 4 digit numbers that follows the (
library(stringr)
str_extract(title, "(?<=\\()[0-9]{4}")
#[1] "2016" "2013" "2015"
Or with regmatches/regexpr
regmatches(title, regexpr("(?<=\\()([0-9]{4})", title, perl = TRUE))
#[1] "2016" "2013" "2015"
data
title <- c("La La Land (2016/I)",
"_The African Americans: Many Rivers to Cross with Henry Louis Gates, Jr._ (2013) _The Black Atlantic (1500-1800) (#1.1)_",
"dfajfj(2015)asdfjuwer f(2017)fa.erewr6")