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Intersection of a string

Posted on 2009-07-12
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Last Modified: 2012-05-07
Is there any method to do intersection on String. Say I have a string:
str = car, apple, car, pencil, orange, apple, cup, coffee

I would like to loop through that string and then retrive only the intersected values. so the result would be:
result = car, apple

Can I do this?? Any idea please.
Thanks!!!
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Comment
Question by:Juuno
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10 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 24834044
That wouldn't be an intersection, that would simply be repeated values
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LVL 86

Expert Comment

by:CEHJ
ID: 24834065
Try something like the following:
        List<String> values = Arrays.asList("car, apple, car, pencil, orange, apple, cup, coffee".split("\\s*,\\s*"));
        Stack<String> s = new Stack<String>();
        Set<String> dups = new HashSet<String>();
        Collections.sort(values);
        s.push("");
        for (String value : values) {
            if (value.equals(s.peek())) {
                dups.add(value);
            }
            else {
                s.push(value);
            }
        }
        System.out.println(dups);

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LVL 92

Expert Comment

by:objects
ID: 24834081
String str = "car,apple,car,pencil,orange,apple,cup,coffee";
Set unique = new HashSet(Arrays.asList(str.split(",")));
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Author Comment

by:Juuno
ID: 24834209
@ objects - thanks. but I want to get repeated values, not to reduce duplicate values. I think my title makes u confuse. Thanks anyway.

@ CEHJ, is there anyway I can also get the values of how many times they are repeated ?

Thanks!!
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LVL 86

Expert Comment

by:CEHJ
ID: 24834240
>>@ CEHJ, is there anyway I can also get the values of how many times they are repeated ?

You can keep a Map and increment the count into it, keyed on the value
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Author Comment

by:Juuno
ID: 24834272
ur code is like: if u find an equal string, then put that value into 'dups', right? so, I tried to change like this:

But it printed out like this: {car=1, apple=1}
String test = "car, apple, car, pencil, orange, apple, cup, coffee";
	       List<String> values = Arrays.asList(test.split("\\s*,\\s*"));
	        Stack<String> s = new Stack<String>();
	        Map<String, Integer> dups = new HashMap<String, Integer>();
	        Collections.sort(values);
	        s.push("");
	        int ctn=0;
	        for (String value : values) {
	            if (value.equals(s.peek())) {
	            	if(dups.get(value) == null) {
				        dups.put(value, new Integer(1));
				    } else {
				    	dups.put(value, new Integer(dups.get(value).intValue() + 1));
				    }
				    }
	            else {
	                s.push(value);
	            }
	        }
	        System.out.println(dups);
	}

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Author Comment

by:Juuno
ID: 24834315
I got it:
I should change the value '1' to '2' in this line:
> dups.put(value, new Integer(1)
> dups.put(value, new Integer(2).

Thanks anyway!!

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LVL 86

Expert Comment

by:CEHJ
ID: 24834371
You first of all need to get the count out of the Map if the key exists, and increment it. If the key doesn't exist, you put a count of 1
0
 
LVL 92

Expert Comment

by:objects
ID: 24834405
> @ objects - thanks. but I want to get repeated values, not to reduce duplicate values.

yes saw that. you just need to remove the unique values from the original list.
you will be left with the values that are diped

let me know if you need the code, should only be a couple of lines, you don't need a loop
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Accepted Solution

by:
ozlevanon earned 2000 total points
ID: 24860852
You can also achieve that using Collections.frequency method (not that most efficient code, but shorter).
See snippet below.
String str = "car, apple, car, pencil, orange, apple, cup, coffee";
List<String> list = new ArrayList<String>(Arrays.asList(str.split("\\s*,\\s*")));
Set<String> duplicates = new HashSet<String>();
for (String s : list)
{
	if (Collections.frequency(list, s) > 1)
	{
		duplicates.add(s);
	}
}
System.out.println("duplicates = " + duplicates);

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