Splitting on comma outside quotes [duplicate]

Question

My program reads a line from a file. This line contains comma-separated text like:

123,test,444,"don't split, this",more test,1 

I would like the result of a split to be this:

123 test 444 "don't split, this" more test 1 

If I use the String.split(","), I would get this:

123 test 444 "don't split  this" more test 1 

In other words: The comma in the substring "don't split, this" is not a separator. How to deal with this?

Answer 1

You can try out this regex:

str.split(",(?=(?:[^\"]*\"[^\"]*\")*[^\"]*$)"); 

This splits the string on , that is followed by an even number of double quotes. In other words, it splits on comma outside the double quotes. This will work provided you have balanced quotes in your string.

Explanation:

,           // Split on comma (?=         // Followed by    (?:      // Start a non-capture group      [^"]*  // 0 or more non-quote characters      "      // 1 quote      [^"]*  // 0 or more non-quote characters      "      // 1 quote    )*       // 0 or more repetition of non-capture group (multiple of 2 quotes will be even)    [^"]*    // Finally 0 or more non-quotes    $        // Till the end  (This is necessary, else every comma will satisfy the condition) ) 

You can even type like this in your code, using (?x) modifier with your regex. The modifier ignores any whitespaces in your regex, so it's becomes more easy to read a regex broken into multiple lines like so:

String[] arr = str.split("(?x)   " +                       ",          " +   // Split on comma                      "(?=        " +   // Followed by                      "  (?:      " +   // Start a non-capture group                      "    [^\"]* " +   // 0 or more non-quote characters                      "    \"     " +   // 1 quote                      "    [^\"]* " +   // 0 or more non-quote characters                      "    \"     " +   // 1 quote                      "  )*       " +   // 0 or more repetition of non-capture group (multiple of 2 quotes will be even)                      "  [^\"]*   " +   // Finally 0 or more non-quotes                      "  $        " +   // Till the end  (This is necessary, else every comma will satisfy the condition)                      ")          "     // End look-ahead                          ); 

Answer 2

Why Split when you can Match?

Resurrecting this question because for some reason, the easy solution wasn't mentioned. Here is our beautifully compact regex:

"[^"]*"|[^,]+ 

This will match all the desired fragments (see demo).

Explanation

• With "[^"]*", we match complete "double-quoted strings"
• or |
• we match [^,]+ any characters that are not a comma.

A possible refinement is to improve the string side of the alternation to allow the quoted strings to include escaped quotes.