Hi, Now that I have read the tutorials, I think that the best way to learn Haskell would be to use the language and write something simple yet useful. I noticed that Haskell lacks a module for reading/writing csv (comma separated value) files, so I thought I could implement that. Questions: 1. Please tell me if you know of a csv module, because then I would do something else. 2. I am looking for a parser, but I don't know Haskell parsers. Is Parsec a good choice? Thanks, Tamas
On Tue, 22 Aug 2006, Tamas K Papp wrote:
Hi,
Now that I have read the tutorials, I think that the best way to learn Haskell would be to use the language and write something simple yet useful. I noticed that Haskell lacks a module for reading/writing csv (comma separated value) files, so I thought I could implement that.
Questions:
1. Please tell me if you know of a csv module, because then I would do something else.
see attachment
On Tue, Aug 22, 2006 at 11:26:45AM +0200, Henning Thielemann wrote:
See also http://www.xoltar.org/languages/haskell.html http://www.xoltar.org/languages/haskell/CSV.hs
Thanks. Haskell is incredibly neat ;-) Now I need to find something else for practice. Is there anything related to data analysis/statistics that is lacking is Haskell? Best, Tamas
Hello Tamas, Tuesday, August 22, 2006, 1:59:28 PM, you wrote:
Now I need to find something else for practice. Is there anything related to data analysis/statistics that is lacking is Haskell?
general String/List library containing search, replace, split and all other general algorithms -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com
Now I need to find something else for practice.
How about writing a CiteULike plugin? For example, what could be really useful is if somebody wrote one for the French open archive HAL. This will give you a nice chance to play maybe with parsing stuff, or one of the HTML/XML libraries, or maybe even simple regular expressions. See: http://www.citeulike.org/faq/all.adp http://hal.inria.fr/index.php?langue=en -- Eric Kow http://www.loria.fr/~kow PGP Key ID: 08AC04F9 Merci de corriger mon français.
Now I need to find something else for practice. Is there anything related to data analysis/statistics that is lacking is Haskell?
A native implementation of multiparameter data fitting (requires some linear algebra) like: Sec 15.4 of http://www.library.cornell.edu/nr/bookcpdf.html or http://www.gnu.org/software/gsl/manual/html_node/Multi_002dparameter-fitting... would be nice, unless it exists. (There might be a GSL binding in Haskell for this but I'd rather use a native library.) Jared. -- http://www.updike.org/~jared/ reverse ")-:"
On Tue, 2006-08-22 at 11:59 +0200, Tamas K Papp wrote:
On Tue, Aug 22, 2006 at 11:26:45AM +0200, Henning Thielemann wrote:
See also http://www.xoltar.org/languages/haskell.html http://www.xoltar.org/languages/haskell/CSV.hs
Thanks. Haskell is incredibly neat ;-)
Now I need to find something else for practice. Is there anything related to data analysis/statistics that is lacking is Haskell?
Best,
Tamas
Maybe a crosstab app? Say, read in some csv data and do a crosstab of it. I was looking at doing one myself quite a while back, but I'm an *ultra-newbie* when it comes to Haskell, and such an app would be a real handful for me... :-) I don't know if it'll help at all (as Python is very different to Haskell) but here's a link to a Python "recipe" which does this - http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/334695 A Haskell equivalent would (imo) be a *great* example/appetiser for Haskell. Very useful for newbies too, as even for a simple thing like reading data line-by-line, it's really useful to have an easy-to-understand example. A crosstab app mightn't be that easy to _do_, but I think it would be easy to understand. Just my 2c worth ... - Andy
Check first MissingH. I remember that it came with some parsing routines for common text formats. Best, Titto
-----Original Message----- From: haskell-cafe-bounces@haskell.org [mailto:haskell-cafe- bounces@haskell.org] On Behalf Of Tamas K Papp Sent: 22 August 2006 10:20 To: Haskell Cafe Subject: [Haskell-cafe] implementing a csv reader
Hi,
Now that I have read the tutorials, I think that the best way to learn Haskell would be to use the language and write something simple yet useful. I noticed that Haskell lacks a module for reading/writing csv (comma separated value) files, so I thought I could implement that.
Questions:
1. Please tell me if you know of a csv module, because then I would do something else.
2. I am looking for a parser, but I don't know Haskell parsers. Is Parsec a good choice?
Thanks,
Tamas _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Hi Tamas,
Questions:
1. Please tell me if you know of a csv module, because then I would do something else.
I think MissingH contains a simple CSV parser, but the server seems to be down.
2. I am looking for a parser, but I don't know Haskell parsers. Is Parsec a good choice?
Parsec is definitely a good choice, but beware that it parses the whole input before returning, thus it may consume a huge batch of memory. As CSV is a line oriented format, you should make your parser lazy. Search the mailing list archive for "lazy parser". Regards, Jens
2. I am looking for a parser, but I don't know Haskell parsers. Is Parsec a good choice?
Parsec is definitely a good choice, but beware that it parses the whole input before returning, thus it may consume a huge batch of memory. As CSV is a line oriented format, you should make your parser lazy. Search the mailing list archive for "lazy parser".
A good trick here is to first use "lines" to break up the input into lines and than map a Parsec parse for each line to those lines (returning a list of Maybe a or ParseError a results). All the best, -- Daan.
Regards,
Jens _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
On Tue, Aug 22, 2006 at 08:59:40AM -0700, Daan Leijen wrote:
2. I am looking for a parser, but I don't know Haskell parsers. Is Parsec a good choice?
Parsec is definitely a good choice, but beware that it parses the whole input before returning, thus it may consume a huge batch of memory. As CSV is a line oriented format, you should make your parser lazy. Search the mailing list archive for "lazy parser".
A good trick here is to first use "lines" to break up the input into lines and than map a Parsec parse for each line to those lines (returning a list of Maybe a or ParseError a results).
You can also create a lazy "many" parser using (get|set)ParserState. The benefit is that this will also work if your elements are not in one-to-one relation with lines and that it automatically takes care of maintaining position in the input (for error messages). lazyMany :: GenParser Char () a -> SourceName -> [Char] -> [a] lazyMany p file contents = lm state0 where Right state0 = parse getParserState file contents lm state = case parse p' "" "" of Left err -> error (show err) Right x -> x where p' = do setParserState state choice [ do eof return [] , do x <- p state' <- getParserState return (x : lm state') ] Best regards Tomasz
L.S., Reading and writing a comma seperated datafile doesn't have to be that complicated; the following is an easy way to read a CSV file into a list of tuples and display the list on screen:
displayTuples = do csvData <- readFile "data.csv" putStrLn $ unlines $ map (show . readTuple) $ lines csvData
readTuple :: String -> (Int, Bool, String) readTuple line = read tuple where tuple = '(' : line ++ ")"
If the file "data.csv" contains the following: 1, True, "Festina lente" 2, False, "Carpe diem" displayTuples displays: (1,True,"Festina lente") (2,False,"Carpe diem") Writing a list of tuples to a CSV file is even simpler:
writeTuples file tuples = writeFile file $ unlines $ map (tail . init . show) tuples
The call:
writeTuples "new.csv" [(1, 'a'), (2, 'b')]
results in a file containg:
1,'a'
2,'b'
(without the leading spaces)
Met vriendelijke groet,
Henk-Jan van Tuyl
--
http://Van.Tuyl.eu/
--
On Tue, 22 Aug 2006 11:19:35 +0200, Tamas K Papp
Hi,
Now that I have read the tutorials, I think that the best way to learn Haskell would be to use the language and write something simple yet useful. I noticed that Haskell lacks a module for reading/writing csv (comma separated value) files, so I thought I could implement that.
Questions:
1. Please tell me if you know of a csv module, because then I would do something else.
2. I am looking for a parser, but I don't know Haskell parsers. Is Parsec a good choice?
Thanks,
Tamas
-- Using Opera's revolutionary e-mail client: https://secure.bmtmicro.com/opera/buy-opera.html?AID=789433
On Aug 23, 2006, at 3:37 PM, Henk-Jan van Tuyl wrote:
L.S.,
Reading and writing a comma seperated datafile doesn't have to be that complicated; the following is an easy way to read a CSV file into a list of tuples and display the list on screen:
"For every complex problem, there is a solution which is simple, neat, and wrong." -- HL Mencken Although it seems straightforward at first, CSV suffers from text escaping complexities, just as does every other general purpose plain- text encoding. Most notably, a newline embedded inside double quotes does not end a record. These issues cause ugly corner cases if you aren't expecting them. And that's just the issues with moving tables of strings around; if those fields have non-string interpretations (dates or numbers or what have you), things get really hairy. To do the "right thing" probably requires perl-ish duck typing :-p See http://www.creativyst.com/Doc/Articles/CSV/CSV01.htm for a semi- authoritative reference on CSV. A related RFC is here: http:// tools.ietf.org/html/rfc4180 Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG
On Wed, 23 Aug 2006, Robert Dockins wrote:
On Aug 23, 2006, at 3:37 PM, Henk-Jan van Tuyl wrote:
L.S.,
Reading and writing a comma seperated datafile doesn't have to be that complicated; the following is an easy way to read a CSV file into a list of tuples and display the list on screen:
"For every complex problem, there is a solution which is simple, neat, and wrong." -- HL Mencken
Although it seems straightforward at first, CSV suffers from text escaping complexities, just as does every other general purpose plain-text encoding. Most notably, a newline embedded inside double quotes does not end a record.
I also think that quotes within quotes are represented by "" rather than \" in CSV.
participants (12)
-
Andy Elvey -
Bulat Ziganshin -
Daan Leijen -
Eric Kow -
Henk-Jan van Tuyl -
Henning Thielemann -
Jared Updike -
Jens Fisseler -
Pasqualino 'Titto' Assini -
Robert Dockins -
Tamas K Papp -
Tomasz Zielonka