Match a regular expression to a character vector

Source: R/package.R

This function is a small wrapper on the regexpr base R function, to provide an API that is easier to use.

re_match(pattern, text, ...)

Arguments

pattern

Regular expression, defaults to be a PCRE expression. See regex for more about regular expressions.

text

Character vector.

...

Additional arguments to pass to regexpr.

Value

A character matrix of the matched (sub)strings. The first column is always the full match. This column is named .match. The result of the columns are capture groups, with appropriate column names, if the groups are named.

Details

Currently only the first occurence of the pattern is used.

Examples

dates <- c("2016-04-20", "1977-08-08", "not a date", "2016",
  "76-03-02", "2012-06-30", "2015-01-21 19:58")
isodate <- "([0-9]{4})-([0-1][0-9])-([0-3][0-9])"
re_match(text = dates, pattern = isodate)
#>      .match                       
#> [1,] "2016-04-20" "2016" "04" "20"
#> [2,] "1977-08-08" "1977" "08" "08"
#> [3,] NA           NA     NA   NA  
#> [4,] NA           NA     NA   NA  
#> [5,] NA           NA     NA   NA  
#> [6,] "2012-06-30" "2012" "06" "30"
#> [7,] "2015-01-21" "2015" "01" "21"

# The same with named groups
isodaten <- "(?<year>[0-9]{4})-(?<month>[0-1][0-9])-(?<day>[0-3][0-9])"
re_match(text = dates, pattern = isodaten)
#>      .match       year   month day 
#> [1,] "2016-04-20" "2016" "04"  "20"
#> [2,] "1977-08-08" "1977" "08"  "08"
#> [3,] NA           NA     NA    NA  
#> [4,] NA           NA     NA    NA  
#> [5,] NA           NA     NA    NA  
#> [6,] "2012-06-30" "2012" "06"  "30"
#> [7,] "2015-01-21" "2015" "01"  "21"