parcr (version 0.5.3)

stringparser: String parser constructor

Description

Produce a string parser based on stringr::str_match(), to be used with match_s().

Usage

stringparser(
  match_pattern,
  reshape = function(x) {
     x
 }
)

Arguments

match_pattern

A regular expression that matches the string.

reshape

A function that takes the character vector of captured strings and modifies it to a desired output. By default this is the identity function.

Details

This function uses stringr::str_match() to produce a string parser. Parsers created with this constructor return the failure signal list() when a string does not match the match_pattern. If the pattern contains captured groups then these groups will be returned as a character vector upon matching. If there is no capture group then the function will return silently upon matching the pattern. You can provide a function to the reshape argument to change the output upon matching.

You always have to wrap the parsers made with this constructor in match_s() to create a parser combinator. I decided not to include this standard pattern in the stringparser constructor itself because it complicates testing of these parsers.

See Also

match_s(), stringr::str_match()

Examples

# single capture group
parse_header <- stringparser("^>(\\w+)")
parse_header(">correct_header")     # returns "correct_header"
parse_header("> incorrect_header")  # returns list()

# multiple capture groups
parse_keyvalue <- stringparser("(\\w+):\\s?(\\w+)")
parse_keyvalue("key1: value1")      # returns c("key1", "value1")

# modify output
parse_keyvalue_df <- stringparser("(\\w+):\\s?(\\w+)",
                                   function(x) data.frame(key = x[1], value = x[2])
                                 )
parse_keyvalue_df("key1: value1")      # returns a data frame