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Thread: How to use recursion to parse groups inside groups in Java?

  1. #1
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    Default How to use recursion to parse groups inside groups in Java?

    I'm just starting with recursion, so if someone can try to help I will very much appreciate it.

    I have the following `String`:
        field1: typeA
        field2: typeA
        field3: typeB
        group1:
            fieldA: typeA
            fieldB: typeB
            subGroup1:
                fieldX: typeB
                fieldY: typeB
            fieldC: typeC
        field4: typeA
        group2:
            fieldA: typeB
            subGroup1:
                fieldX: typeA
                fieldY: typeA
            fieldB: typeA
            fieldC: typeC
        field5: typeC
        field6: typeD
    Note that I can have groups inside groups (subgroups). I can also have groups inside groups inside groups, so recursion is mandatory as far as I know.

    Note that the *spacing* in the beginning of each line determines if the field belongs to the group or not.

    I would like to write a method in Java that will return a `LinkedHashMap<String, Object>`, where the *Object* map value can either be a `String` denoting that this is a field (not a group) or another `LinkedHashMap<String, Object>` denoting that this is a group (not a field).

    I've tried but failed miserably. Recursion is just too hard for me at the moment, but I'm studying it.

    To help whoever wants to help, below the code:
        	public static void main(String[] args) {
     
        		String text = String.join("\n",
     
        				"field1: typeA",
        				"field2: typeA",
        				"field3: typeB",
        				"group1:",
        				"    fieldA: typeA",
        				"    fieldB: typeB",
        				"    subGroup1:",
        				"        fieldX: typeB",
        				"        fieldY: typeB",
        				"    fieldC: typeC",
        				"field4: typeA",
        				"group2:",
        				"    fieldA: typeB",
        				"    subGroup1:",
        				"        fieldX: typeA",
        				"        fieldY: typeA",
        				"    fieldB: typeA",
        				"    fieldC: typeC",
        				"field5: typeC",
        				"field6: typeD",
     
        				"");
     
        		Map<String, Object> solution = doIt(text);
        		System.out.println(solution);
        	}
     
        	private static LinkedHashMap<String, Object> doIt(String text) {
        		// solution goes here...
        		return null;
        	}
        }

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: How to use recursion to parse groups inside groups in Java?

    I've tried but failed miserably.
    Can you post the code you tried?

    Be sure to add some comments to the code describing what it is supposed to do.
    Also an example of the output would be useful.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: How to use recursion to parse groups inside groups in Java?

    Can you post the code you tried?
    I have nothing good to show. I got stuck, my brain went into a deadlock!


    Here is the correct output:
        public static void main(String[] args) {
        	Map<String, Object> map = new LinkedHashMap<String, Object>();
     
        	map.put("field1", "typeA");
        	map.put("field2", "typeA");
        	map.put("field3", "typeB");
     
        	Map<String, Object> map2 = new LinkedHashMap<String, Object>();
        	map2.put("fieldA", "typeA");
        	map2.put("fieldB", "typeB");
     
        	Map<String, Object> map3 = new LinkedHashMap<String, Object>();
        	map3.put("fieldX", "typeB");
        	map3.put("fieldY", "typeB");
        	map2.put("subGroup1", map3);
     
        	map2.put("fieldC", "typeC");
     
        	map.put("group1", map2);
     
        	map.put("field4", "typeA");
     
        	Map<String, Object> map4 = new LinkedHashMap<String, Object>();
        	map4.put("fieldA", "typeB");
     
        	Map<String, Object> map5 = new LinkedHashMap<String, Object>();
        	map5.put("fieldX", "typeA");
        	map5.put("fieldY", "typeA");
        	map4.put("subGroup1", map5);
     
        	map4.put("fieldB", "typeA");
        	map4.put("fieldC", "typeC");
     
        	map.put("group2", map4);
     
        	map.put("field5", "typeC");
        	map.put("field6", "typeD");
     
        	System.out.println(map);
        }
    The map matches the original text as you can see below:
    {field1=typeA, field2=typeA, field3=typeB, group1={fieldA=typeA, fieldB=typeB, subGroup1={fieldX=typeB, fieldY=typeB}, fieldC=typeC}, field4=typeA, group2={fieldA=typeB, subGroup1={fieldX=typeA, fieldY=typeA}, fieldB=typeA, fieldC=typeC}, field5=typeC, field6=typeD}

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: How to use recursion to parse groups inside groups in Java?

    I'm not good at recursive either. This site has lots of programmers that like to show off their programming skills. Try them:
    http://www.coderanch.com/forums
    If you don't understand my answer, don't ignore it, ask a question.

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