Simple delimiter parser

Question

I'm trying out PetitParser for parsing a simple integer list delimited by commas. For example: "1, 2, 3, 4"

I tried creating a integer parser and then use the delimitedBy method.

Parser integerParser = digit().plus().flatten().trim().map((String value) -> Integer.parseInt(value));
Parser listParser = integerParser.delimitedBy(of(','));

List<Integer> list = listParser.parse(input).get();

This returns a list with the parsed integers but also the delimiters. For example: [1, ,, 2, ,, 3, ,, 4]

Is there a way to exclude the delimiters from the result?

Do you need this `Parser` for it? You can do it without any external library... — deHaar, Aug 08 '19 at 13:31
Try this: List integerList = Arrays.stream("1, 2, 3, 4".split(",")) .map(i -> Integer.parseInt(i.trim())) .collect(Collectors.toList()); — arifng, Aug 08 '19 at 13:55
I'm aware that this is simple enough to implement with pure java. I'm trying a simple parse because I'm new to PetitParser. — Miguel Figueiredo, Aug 08 '19 at 18:30

score 2 · Accepted Answer · answered Aug 09 '19 at 20:47

2

Yes, there is:

Parser listParser = integerParser
    .delimitedBy(of(','))
    .map(withoutSeparators());

To get withoutSeparators() import import static org.petitparser.utils.Functions.withoutSeparators;.

answered Aug 09 '19 at 20:47

Lukas Renggli

8,754
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score 0 · Answer 2 · answered Aug 08 '19 at 14:52

Here is an example of how to do it without any external library:

public static void main(String args[]) {
    // source String
    String delimitedNumbers = "1, 2, 3, 4, 5, 6, 7, 8, 9, 10";
    // split this String by its delimiter, a comma here
    String[] delimitedNumbersSplit = delimitedNumbers.split(",");

    // provide a data structure that holds numbers (integers) only
    List<Integer> numberList = new ArrayList<>();

    // for each part of the split list
    for (String num : delimitedNumbersSplit) {
        // remove all whitespaces and parse the number
        int n = Integer.parseInt(num.trim());
        // add the number to the list of numbers
        numberList.add(n);
    }

    // then create the representation you want to print
    StringBuilder sb = new StringBuilder();
    // [Java 8] concatenate the numbers to a String that delimits by whitespace
    numberList.forEach(number -> sb.append(number).append(" "));
    // then remove the trailing whitespace
    String numbersWithoutCommas = sb.toString();
    numbersWithoutCommas = numbersWithoutCommas.substring(0, numbersWithoutCommas.length() - 1);
    // and print the result
    System.out.println(numbersWithoutCommas);
}

Note that you don't need to trim() the results of the split String if you have a list without whitespaces.

In case you need the PetitParser library, you will have to look up how to use it in its docs.

Thanks for the reply. The goal here is to try out PetitParser with simple examples. Unfortunately the documentation is not detailed. I have to dig in the source code ;) — Miguel Figueiredo, Aug 08 '19 at 19:27

score 0 · Answer 3 · answered Aug 09 '19 at 00:37

With a bit more code I got the result without the delimiters:

Parser number = digit().plus().flatten().trim()
        .map((String value) -> Integer.parseInt(value));

Parser next = of(',').seq(number).map((List<?> input) -> input.get(1)).star();

Parser parser = number.seq(next).map((List<List<?>> input) -> {
    List<Object> result = new ArrayList<>();
    result.add(input.get(0));
    result.addAll(input.get(1));
    return result;
});

Simple delimiter parser

3 Answers3