Parsing a comma-separated file

Hi, I had a question about parsing just one line at a time beforehand
and now I'm working on a program to parse multiple items on each
line-something like the following:

name, age, gender
Bob, 32, M
Stacy, 14, F
...
...

How do I parse 'Bob', knowing it's the first element on the line, '32'
is the second, 'M' is the last...I've been reading about regular
expressions. Is this the best way to solve this problem? And how exactly
do you use them?

Thanks!!

···

--
Posted via http://www.ruby-forum.com/.

Are you looking for this?
http://fastercsv.rubyforge.org/

Ruby also has the csv standard library.

Regards,
Thomas.

name, age, gender
Bob, 32, M
Stacy, 14, F
...
How do I parse 'Bob', knowing it's the first element on the line, '32'
is the second, 'M' is the last...I've been reading about regular
expressions. Is this the best way to solve this problem? And how exactly
do you use them?

This doesn't handle all CSV specs, but if you know you have pure data
like you show above, these are the rudimentary steps without the
one-liner tricks, so it should be pretty straight forward to understand
each step. Arranging them as methods to a class would be good.

# read the file into a var

  if FileTest::exist?(file_name)
    file_lines = IO.readlines(file_name)
  end

# normalize line endings so it doesn't matter what they are

  file_lines.strip!
  file_lines.gsub!(/\r\n/,'\n')
  file_lines.gsub!(/\r/,'\n')

# normalize comma delimiters so it doesn't matter
# if you have one, two or one,two or one , two etc...

   file_lines.gsub!(/\s*,\s*/, ',')

# split lines into a single array of lines

  lines_array = file_lines.split('\n')

# split each line into an array

  final_data =

  lines_array.each do |this_line|
    final_data << this_line.split(',')
  end

# final_data is now an array of arrays that looks like this:

  [
    ['name', 'age', 'gender'],
    ['Bob', '32', 'M'],
    ['Stacy', '14', 'F']
  ]

So, to get Bob, you'd have to know his line number, and index into the
record array:

  final_data[1][0] # Bob
  final_data[2][3] # F

-- greg willits

···

--
Posted via http://www.ruby-forum.com/\.

ThoML wrote:

Are you looking for this?
http://fastercsv.rubyforge.org/

Ruby also has the csv standard library.

Regards,
Thomas.

That is great Thomas! Although, I'd like to know how to do it with the
regular expressions as well.

Thanks!

···

--
Posted via http://www.ruby-forum.com/\.

  final_data[1][0] # Bob
  final_data[2][3] # F

should the last one be:
  final_data[2][2] # F
??

Thanks! Also, is this an effective way to parse a large file. What if I
had to read a million lines with multiple columns? Would this solution
still be practical?

Thanks again!

···

--
Posted via http://www.ruby-forum.com/\.

I'd recommend using Sring#split. In the simplest case you could just
specify line.split(','); no regular expressions needed. If you wanted
you could use a regular expression argument to #split in order to skip
whitespace:

  line.split(/\s*,\s*/)

but you could just as easily trim the values after the fact too:

  line.split(',').map{|v| v.strip}

Regular expressions are not the best solution for parsing CSV,
especially once you start dealing with quoted values.

···

On Mon, Jun 9, 2008 at 12:46 PM, Justin To <tekmc@hotmail.com> wrote:

That is great Thomas! Although, I'd like to know how to do it with the
regular expressions as well.

--
Avdi

Home: http://avdi.org
Developer Blog: Avdi Grimm, Code Cleric
Twitter: http://twitter.com/avdi
Journal: http://avdi.livejournal.com

So is the fasterCSV the most effective way of parsing a comma-separated
file?

···

--
Posted via http://www.ruby-forum.com/.

It is the fastest and most robust way.

···

On Mon, Jun 9, 2008 at 2:08 PM, Justin To <tekmc@hotmail.com> wrote:

So is the fasterCSV the most effective way of parsing a comma-separated
file?

--
Avdi

Home: http://avdi.org
Developer Blog: http://avdi.org/devblog/
Twitter: http://twitter.com/avdi
Journal: http://avdi.livejournal.com

My experience (at least a year ago) was that fastercsv was a great way to go if you had very clean files without errors, odd characters, etc. Unfortunately, I had files that were a bit more problematic and so I ended up using a combination of either parsing it myself (split, regexs. etc) and catching all the errors and handling them or using the parse_line method in the standard csv library.

···

On Jun 9, 2008, at 2:09 PM, Avdi Grimm wrote:

On Mon, Jun 9, 2008 at 2:08 PM, Justin To <tekmc@hotmail.com> wrote:

So is the fasterCSV the most effective way of parsing a comma-separated
file?

It is the fastest and most robust way.

--
Avdi

Home: http://avdi.org
Developer Blog: http://avdi.org/devblog/
Twitter: http://twitter.com/avdi
Journal: http://avdi.livejournal.com

Great guys, thanks for the help!

···

--
Posted via http://www.ruby-forum.com/.

FasterCSV has a parse_line() method as well, just FYI.

James Edward Gray II

···

On Jun 9, 2008, at 4:52 PM, Charles Walden wrote:

My experience (at least a year ago) was that fastercsv was a great way to go if you had very clean files without errors, odd characters, etc. Unfortunately, I had files that were a bit more problematic and so I ended up using a combination of either parsing it myself (split, regexs. etc) and catching all the errors and handling them or using the parse_line method in the standard csv library.