how to extract the first number from each string in a vector in R?

Question

I am new to regex in R. Here I have a vector where I am interested in extracting the first occurance of a number in each string of the vector .

I have a vector calle

Answer 1

You can do this very nicely with the str_first_number() function from the strex package, or for more general needs, there's the str_nth_number() function.

pacman::p_load(strex)
shootsummary <- c("Aaron Alexis, 34, a military veteran and contractor ...",
                  "Pedro Vargas, 42, set fire to his apartment, killed six ...",
                  "John Zawahri, 23, armed with a homemade assault rifle ...",
                  "John Zawahri, 23, armed with a homemade assault rifle ...",
                  "Dennis Clark III, 27, shot and killed his girlfriend ...",
                  "Kurt Myers, 64, shot six people in neighboring ..."
)
str_first_number(shootsummary)
#> [1] 34 42 23 23 27 64
str_nth_number(shootsummary, n = 1)
#> [1] 34 42 23 23 27 64

Created on 2018-09-03 by the reprex package (v0.2.0).

Answer 2

One option is str_extract from stringr with an as.numeric wrap.

> library(stringr)
> as.numeric(str_extract(shootsummary, "[0-9]+"))
# [1] 34 42 23 27 64

Update In response to your question in the comments of this answer, here's a little explanation. The full explanation of a function can be found in its help file.

• str_extract returns the first occurrence of the regular expression. It is vectorized over the character vector in its first argument.
• The regular expression [0-9]+ matches any character of: '0' to '9' (1 or more times)
• as.numeric changes the resulting character vector into a numeric vector.

Answer 3

R's regmatches() method returns a vector with the first regex match in each element:

regmatches(shootsummary, regexpr("\\d+", shootsummary, perl=TRUE));

Answer 4

how about

splitbycomma <- strsplit(shootsummary, ",")
as.numeric(  sapply(splitbycomma, "[", 2)  )

Answer 5

You could try the below sub command,

> test
[1] "Aaron Alexis, 34, a military veteran and contractor from Texas, opened fire in the Navy installation, killing 12 people and wounding 8 before being shot dead by police."              
[2] "Pedro Vargas, 42, set fire to his apartment, killed six people in the complex, and held another two hostages at gunpoint before a SWAT team stormed the building and fatally shot him."
> sub("^\\D*(\\d+).*$", "\\1", test)
[1] "34" "42"

Pattern Explanation:

• ^ asserts that we are at the start of a line.
• \D* Matches zero or more non-digit characters.
• (\d+) then the following one or more digits is captured into group 1(first number).
• .* Matches any character zero or more times.
• $ Asserts that we are at the end of a line.
• Finally all the matched chars are replaced by the chars which are present inside the first group .

Answer 6

stringi would be faster

library(stringi)
stri_extract_first(shootsummary, regex="\\d+")
#[1] "34" "42" "23" "27" "64"