The following is my second attempt at a basic CSV parser in Ruby. I've addressed suggestions that I've got for my previous version here.
I have omitted all test cases - the code listing would be too long otherwise. You can look at the full code-base at GitHub if you want to.
As opposed to the last version, the current solution supports:
- multiple different value delimiters,
- values surrounded by quotes,
- delimiters as a part of quoted values,
- quotes as a part of quoted values.
Please note that my intentions are not to implement a full-featured CSV parser, but to improve my Ruby programming skills. I'll appreciate any suggestions.
csv_parser.rb
require_relative 'line_parser'
# An exception to report that the given delimiter is not supported.
#
class UnsupportedDelimiterException < Exception
attr_reader :delimiter
def initialize delimiter
@delimiter = delimiter
end
def to_s
"Unsupported delimiter [#{@delimiter}]."
end
end
# CSV file parser.
#
# USAGE:
# CsvFile.new(';').parse('data.csv').each { |row| puts row.firstname }
#
class CsvFile
SUPPORTED_DELIMITERS = [ ",", "|", ";", " ", " "]
DEFAULT_DELIMITER = ","
# Initializes the parser.
#
# * *Args* :
# - +delimiter+ -> The character to be used as delimiter. Defaults to
# DEFAULT_DELIMITER. Must be one of SUPPORTED_DELIMITERS, otherwise
# an UnsupportedDelimiterException is raised.
#
def initialize delimiter = DEFAULT_DELIMITER
if not SUPPORTED_DELIMITERS.include? delimiter
raise UnsupportedDelimiterException.new delimiter
end
@line_parser = LineParser.new(Lexer.new delimiter)
end
# Parses the given CSV file and returns the result as an array of rows.
#
def parse file
rows = []
headers = @line_parser.parse file.gets.chomp
file.each do |line|
values = {}
headers.zip(@line_parser.parse line.chomp).each do |key, value|
values[key] = value
end
rows << CsvRow.new(values)
end
rows
end
end
# CSV row.
#
class CsvRow
# Creates a new CSV row with the given values.
#
# * *Args* :
# - +values+ -> a hash containing the column -> value mapping
#
def initialize values
@values = values
end
# Returns the value in the column given as method name, or null if
# no such value exists.
#
def method_missing name, *args
@values[name.to_s]
end
end
line_parser.rb
require_relative 'lexer'
class ParseError < RuntimeError
end
# CSV line parser.
#
class LineParser
# Initializes the parser with the given lexer instance.
#
def initialize lexer
@lexer = lexer
end
# Parses the given CSV line into a collection of values.
#
def parse line
values = []
last_seen_identifier = false
tokens = @lexer.tokenize line
tokens.each do |token|
case token
when EOFToken
if not last_seen_identifier
values << ""
end
break
when DelimiterToken
if not last_seen_identifier
values << ""
next
else
last_seen_identifier = false
end
when IdentifierToken
if last_seen_identifier
raise ParseError, "Unexpected identifier - a delimiter was expected."
end
last_seen_identifier = true
values << token.lexem
end
end
values
end
end
lexer.rb
require_relative 'assertions'
class LexicalError < RuntimeError
end
class Token
end
class EOFToken < Token
def to_s
"EOF"
end
end
class DelimiterToken < Token
attr_reader :lexem
def initialize lexem
@lexem = lexem
end
def to_s
"DELIMITER(#{@lexem})"
end
end
class IdentifierToken < Token
attr_reader :lexem
def initialize lexem
@lexem = lexem
end
def to_s
"IDENTIFIER(#{@lexem})"
end
end
# CSV line lexical analyzer.
#
class Lexer
# Initialzes the lexer.
#
# * *Args* :
# - +delimiter+ -> The character to be used as delimiter.
#
def initialize delimiter
@delimiter = delimiter
end
# Breaks the given CSV line into a sequence of tokens.
#
def tokenize stream
stream = stream.chars.to_a
tokens = []
while true
tokens << next_token(stream)
if tokens.last.is_a? EOFToken
break
end
end
tokens
end
private
def next_token stream
char = stream.shift
case char
when eof
EOFToken.new
when delimiter
DelimiterToken.new delimiter
when quotes
stream.unshift char
get_quoted_identifier stream
else
stream.unshift char
get_unquoted_identifier stream
end
end
def get_unquoted_identifier stream
lexem = ""
while true do
char = stream.shift
case char
when delimiter
stream.unshift char
return IdentifierToken.new lexem
when eof
return IdentifierToken.new lexem
else
lexem << char
end
end
end
def get_quoted_identifier stream
char = stream.shift
assert { char == quotes }
lexem = ""
while true do
char = stream.shift
case char
when eof
raise LexicalError, "Unexpected EOF within a quoted string."
when quotes
if stream.first == quotes
lexem << quotes
stream.shift
else
return IdentifierToken.new lexem
end
else
lexem << char
end
end
end
def eof
nil
end
def delimiter
@delimiter
end
def quotes
'"'
end
end
assertions.rb
# An exception to represent assertion violations.
#
class AssertionError < RuntimeError
end
# Evaluates the given block as a boolean expression and throws an AssertionError
# in case it results to false.
#
def assert &block
raise AssertionError unless yield
end
