CSV Parsing

Question

I am trying to use C# to parse CSV. I used regular expressions to find \",\" and read string if my header counts were equal to my match count.

Now this

Answer 1

FileHelpers for .Net is your friend.

Answer 2

Well, I'm no regex wiz, but I'm certain they have an answer for this.

Procedurally it's going through letter by letter. Set a variable, say dontMatch, to FALSE.

Each time you run into a quote toggle dontMatch.

each time you run into a comma, check dontMatch. If it's TRUE, ignore the comma. If it's FALSE, split at the comma.

This works for the example you give, but the logic you use for quotation marks is fundamentally faulty - you must escape them or use another delimiter (single quotes, for instance) to set major quotations apart from minor quotations.

For instance,

"a", ""b", ""c", "d"", "e""

will yield bad results.

This can be fixed with another patch. Rather than simply keeping a true false you have to match quotes.

To match quotes you have to know what was last seen, which gets into pretty deep parsing territory. You'll probably, at that point, want to make sure your language is designed well, and if it is you can use a compiler tool to create a parser for you.

-Adam

Answer 3

The Lumenworks CSV parser (open source, free but needs a codeproject login) is by far the best one I've used. It'll save you having to write the regex and is intuitive to use.

Answer 4

If all your values are guaranteed to be in quotes, look for values, not for commas:

("".*?""|"[^"]*")

This takes advantage of the fact that "the earliest longest match wins" - it looks for double quoted values first, and with a lower priority for normal quoted values.

If you don't want the enclosing quote to be part of the match, use:

"(".*?"|[^"]*)"

and go for the value in match group 1.

As I said: Prerequisite for this to work is well-formed input with guaranteed quotes or double quotes around each value. Empty values must be quoted as well! A nice side-effect is that it does not care for the separator char. Commas, TABs, semi-colons, spaces, you name it. All will work.

Answer 5

Try CsvHelper (a library I maintain) or FastCsvReader. Both work well. CsvHelper does writing also. Like everyone else has been saying, don't roll your own. :P

Answer 6

I have just try your regular expression in my code..its work fine for formated text with quote ...

but wondering if we can parse below value by Regex..

"First_Bat7679",""NAME","ENAME","FILE"","","","From: "DDD,_Ala%as"@sib.com"

I am looking for result as:

'First_Bat7679'
'"NAME","ENAME","FILE"'
''
''
'From: "DDD,_Ala%as"@sib.com'

Thanx