5 ms·

You can replace all commas with a placeholder (e.g. "#COMMA#"), replace the delimiter with a comma, parse the document and then replace all placeholders in the

You can replace all commas with a placeholder (e.g. "#COMMA#"), replace the delimiter with a comma, parse the document and then replace all placeholders in the data with ",".

Someone 12y ago
That does not work, unless that first replacement magically ignores the commas that are part of field separators. If you know how to write the code that does that, your problem is solved.
- lignuist 12y ago
  I was referencing to "What if the character separating fields is not a comma?". And there it clearly works. I used this technique a few times with success. If you find a CSV file that has mixed field separator types, then you probably found a broken CSV file.
  - zAy0LfpBZLC8mAC 12y ago
    No, it doesn't. What if there is #COMMA# in one of the fields?
    - lignuist 12y ago
      You just choose a placeholder that does not appear in the data. You could even implement it in a way that a placeholder is automatically selected upfront that does not appear in the data. When it comes to parsing, the thing is that you usually have to make some assumptions about the document structure.
      - zAy0LfpBZLC8mAC 12y ago
        What if there is #COMMA, in one of the fields (but no #COMMA#)? Yes, the assumption you have to make is called the grammar, and you better have a parser that always does what the grammar says, and global text replacement is a technique that is easy to get wrong, difficult to prove correct, and completely unnecessary at that.
        lignuist 12y ago
        > What if there is #COMMA, in one of the fields (but no #COMMA#)? What should happen? Since #COMMA is not #COMMA#, it gets not replaced, because it does not match. Please keep in mind, that I replied to suni's very specific question and did not try to start a discussion about general parser theory. In practice, we find a lot of files that do not respect the grammar, but still need to find a way to make the data accessible.
        zAy0LfpBZLC8mAC 12y ago
        What would happen is that you first would replace #COMMA, with #COMMA#COMMA# and then later replace that with ,COMMA# , thus garbling the data. The way to make the data accessible is to request the producer to be fixed, it's that simple. If that is completely impossible, you'll have to figure out the grammar of the data that you actually have and build a parser for that. Your suggested strategy does not work.
        lignuist 12y ago
        I used that strategy for parsing gigabytes of CSVs containing arbitrary natural language from the web - try to get these files fixed, or figure out a grammar for gigabytes of fuzzy data... My approach never failed for me, so telling me that my strategy does not work is a strong claim, where it reliably did the job for me. Your examples are all valid, but what you are describing are theoretical attacks on the method, while the method works in almost all cases in practice. We are talking about two different viewpoints: dealing with large amounts of messy data on one hand and parser theory in an ideal cosmos on the other hand.
        zAy0LfpBZLC8mAC 12y ago
        How do you know that the strategy worked reliably if you never compared the results to the results obtained using a reliable method (which you presumably didn't, because then you could just have used the reliable method)? The larger the data you have to deal with, the more likely it is that corner cases will occur in it, and the less likely that you will notice anomalies, thus the more important that you are very strict in your logic if you want to derive any meaningful results. As such, the two viewpoints really are: not really caring about the soundness of your results and solving the actual problem. Now, maybe you really can show that the bugs in the methods you use only cause negligible noise in your results, in which case it might be perfectly fine to use those methods. But just ignoring errors in your deduction process because you don't feel like doing the work of actually solving the problem at hand is not pragmatism. You'll have to at least demonstrate that your approach does not invalidate the result.

You can replace all commas with a placeholder (e.g. "#COMMA#"), replace the delimiter with a comma, parse the document and then replace all placeholders in the data with ",".

Someone 12y ago

That does not work, unless that first replacement magically ignores the commas that are part of field separators. If you know how to write the code that does that, your problem is solved.

lignuist 12y ago
I was referencing to "What if the character separating fields is not a comma?". And there it clearly works. I used this technique a few times with success. If you find a CSV file that has mixed field separator types, then you probably found a broken CSV file.
- zAy0LfpBZLC8mAC 12y ago
  No, it doesn't. What if there is #COMMA# in one of the fields?
  - lignuist 12y ago
    You just choose a placeholder that does not appear in the data. You could even implement it in a way that a placeholder is automatically selected upfront that does not appear in the data. When it comes to parsing, the thing is that you usually have to make some assumptions about the document structure.
    - zAy0LfpBZLC8mAC 12y ago
      What if there is #COMMA, in one of the fields (but no #COMMA#)? Yes, the assumption you have to make is called the grammar, and you better have a parser that always does what the grammar says, and global text replacement is a technique that is easy to get wrong, difficult to prove correct, and completely unnecessary at that.
      - lignuist 12y ago
        > What if there is #COMMA, in one of the fields (but no #COMMA#)? What should happen? Since #COMMA is not #COMMA#, it gets not replaced, because it does not match. Please keep in mind, that I replied to suni's very specific question and did not try to start a discussion about general parser theory. In practice, we find a lot of files that do not respect the grammar, but still need to find a way to make the data accessible.
        zAy0LfpBZLC8mAC 12y ago
        What would happen is that you first would replace #COMMA, with #COMMA#COMMA# and then later replace that with ,COMMA# , thus garbling the data. The way to make the data accessible is to request the producer to be fixed, it's that simple. If that is completely impossible, you'll have to figure out the grammar of the data that you actually have and build a parser for that. Your suggested strategy does not work.
        lignuist 12y ago
        I used that strategy for parsing gigabytes of CSVs containing arbitrary natural language from the web - try to get these files fixed, or figure out a grammar for gigabytes of fuzzy data... My approach never failed for me, so telling me that my strategy does not work is a strong claim, where it reliably did the job for me. Your examples are all valid, but what you are describing are theoretical attacks on the method, while the method works in almost all cases in practice. We are talking about two different viewpoints: dealing with large amounts of messy data on one hand and parser theory in an ideal cosmos on the other hand.
        zAy0LfpBZLC8mAC 12y ago
        How do you know that the strategy worked reliably if you never compared the results to the results obtained using a reliable method (which you presumably didn't, because then you could just have used the reliable method)? The larger the data you have to deal with, the more likely it is that corner cases will occur in it, and the less likely that you will notice anomalies, thus the more important that you are very strict in your logic if you want to derive any meaningful results. As such, the two viewpoints really are: not really caring about the soundness of your results and solving the actual problem. Now, maybe you really can show that the bugs in the methods you use only cause negligible noise in your results, in which case it might be perfectly fine to use those methods. But just ignoring errors in your deduction process because you don't feel like doing the work of actually solving the problem at hand is not pragmatism. You'll have to at least demonstrate that your approach does not invalidate the result.