Replace string using Regex replace pattern

Question

Basically I am dealing with CSV file and reading it line by line in C#. I have a string input(a line) and trying to find a Regex pattern and replace it using another Regex pattern but result is not what I expect.

var input = "\"efgh ,ijkl123,\",abcd ,  \"efgh ,ijkl123,\",mnop456 \"efgh ,ijkl123,\"";

In output I need to replace internal commas between double quotations with semicolon where those double quotation are between commas themselves.

between double quotation and external comma (comma outside of pair of double quotes) it can be only white space.

So I expect output to be: "efgh ;ijkl123,",abcd , "efgh ;ijkl123,",mnop456 "efgh ,ijkl123,"

my code:

var pattern = @".*,\s*""(.*,+.*)+""\s*,.*";
var replacePattern = @".*,\s*""(.*;+.*)+""\s*,.*";
if (Regex.IsMatch(input, pattern))
{
    var output = Regex.Replace(input, pattern, replacePattern);
}

but running my code, output is: .,\s"(.;+.)+"\s*,.* which is replacePattern.

EDIT more input sample and output as expected:

input abcd , "efgh ,ijkl123,",mnop456

output abcd , "efgh ;ijkl123;",mnop456
input "efgh ,ijkl123,",abcd , "efgh ,ijkl123,",mnop456 "efgh ,ijkl123,"

output "efgh ;ijkl123;",abcd , "efgh ;ijkl123;",mnop456 "efgh ,ijkl123,"
input ,"efgh ,ijkl123,",abcd" , "efgh ijkl123,",mnop456 "efgh ,ijkl123,","efgh ,ijkl123,"mnop456

output ,"efgh ;ijkl123;",abcd" , "efgh ijkl123;",mnop456 "efgh ,ijkl123,","efgh ,ijkl123,"mnop456
input ,"efgh" ,ijkl123,",abcd" , "efgh ijkl123,",mnop456 "efgh ,ijkl123,","efgh ,ijkl123,"mnop456

output ,"efgh" ,ijkl123,";abcd" , "efgh ijkl123;",mnop456 "efgh ,ijkl123,","efgh ,ijkl123,"mnop456
input efgh ,ijkl123,",abcd , "efgh ,ijkl123,",mnop456 "efgh ,ijkl123,"

output efgh ,ijkl123,",abcd , "efgh ;ijkl123;",mnop456 "efgh ,ijkl123,"

What I'm reading from your statement is that you want to replace , coma with ; semi colon if it's between double quotes? — Saleem
– Saleem, Commented Apr 14, 2016 at 2:05
What's the expect behavior if the string have more than 2 double quotes ? — Zee
– Zee, Commented Apr 14, 2016 at 2:09
yeah and that pair of double quotes are between comma as well. if I want to simplify, it would be like this: , " , " , => , " ; " , — Amir Chatrbahr
– Amir Chatrbahr, Commented Apr 14, 2016 at 2:09
@Zee I need to find any pair of double quotes in input. so it could be 2, 4, 6,... double quotes. — Amir Chatrbahr
– Amir Chatrbahr, Commented Apr 14, 2016 at 2:12

Saleem · Accepted Answer · 2016-04-15 02:25:57Z

1

Well, this is bit tricky and I'm sure someone will suggest a better regex than mine. Suppose you input text is:

"efgh ,ijkl123,",abcd ,  "efgh ,ijkl123,",mnop456 "efgh ,ijkl123,"

You can try:

var data = "\"efgh ,ijkl123,\",abcd ,  \"efgh ,ijkl123,\",mnop456 \"efgh ,ijkl123,\"";

var rx = @"(?<=(^|,[ \t]*))\""[^\""\n]+\""(?=[ \t]*(,|$))";

var matches = Regex.Matches (data, rx);

foreach (Match match in matches) {
    data = new Regex (match.Value).
        Replace(data, match.Value.Replace (',', ';'), 1);
}

Console.WriteLine (data);

It will emit:

"efgh ;ijkl123;",abcd ,  "efgh ;ijkl123;",mnop456, "efgh ,ijkl123,"

Code above is essentially replacing all , comas between double quotes with ; semi colons.

edited Apr 15, 2016 at 2:25

answered Apr 14, 2016 at 2:41

Saleem

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10 Comments

Amir Chatrbahr Over a year ago

nice one! but in your example it should be 2 matches not 3. the last one shouldn't match because what I want is that between external comma (comma outside of pair of double quotes) and double quotation it can be only white space.

Saleem Over a year ago

hmm, well in that case my sample input is incorrect. it's not a valid CSV file. Can you give it a try with valid string and see how it goes. You can try in regex101 (link is posted above). Anyway, I have updated my sample input and expected output strings.

Amir Chatrbahr Over a year ago

no your sample input was great and it was a standard CSV format. I am going to adopt it as my input.

Saleem Over a year ago

It should even work with a tricky CSV. efgh ,ijkl123,",abcd , "efgh ,ijkl123,",mnop456 "efgh ,ijkl123,". Note single double quote.

Amir Chatrbahr Over a year ago

no unfortunately I get this: efgh ;ijkl123;",abcd , "efgh ,ijkl123,",mnop456 "efgh ,ijkl123,"

|

Hari Prasad · Accepted Answer · 2016-04-14 04:34:25Z

0

Not sure is it very efficient, but works. Suggestions are welcome to improve it further.

string  input = "\"efgh ,ijkl123,\",abcd ,  \"efgh ,ijkl123,\",mnop456 \"efgh ,ijkl123,\"";; 

Regex.Matches(input, "\"([^\"]*)\"(,)") // Extract string between quotes followed by ','.
.Cast<Match>()
    .ToList()
    .ForEach(m=> input = input.Replace(m.Value, m.Value.Replace(",",";")) // for each match replace with ';' inserted match.
                              .Replace(";\";",",\","));  // a hack, should have done it better

Ouput :

"efgh ;ijkl123,",abcd ,  "efgh ;ijkl123,",mnop456 "efgh ,ijkl123,"

Working Demo

edited Apr 14, 2016 at 4:34

answered Apr 14, 2016 at 3:09

Hari Prasad

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3 Comments

Amir Chatrbahr Over a year ago

Thanks! I just edited my post. between double quotation and external comma (comma outside of pair of double quotes) it can be only white space. so if I use this input in your code, I expect 2 replaces not 3: var input = "\"efgh ,ijkl123,\",abcd , \"efgh ,ijkl123,\",mnop456 \"efgh ,ijkl123,\"";

Amir Chatrbahr Over a year ago

it didn't work for this: "\"efgh ,ijkl123,\",abcd , \"efgh ,ijkl123,\",mnop456 \"efgh ,ijkl123,\"" i got "\"efgh ;ijkl123,\",abcd , \"efgh ;ijkl123,\",mnop456 \"efgh ,ijkl123,\""

Hari Prasad Over a year ago

What is expected for this string? seems working as expected to me.

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