Sort the rows of a file according to an integer

[ze snow]

Hi guys,

I have a file with about 7'000 rows. Each row has 6 fields (words or numbers), all separated by a space, like this :

field1 field2 field3 field4 field5 field6

I would like to sort all these lines according to the 3rd field which is actually an "int".

I saw that people use the class Comparator and rewrite the method "compare" inside it but I don't understand how to apply it to my program. My idea is to first read the file and store all these lines into an ArrayList and then sort this ArrayList according to the 3rd field of each member of the ArrayList.

That's what I tried by adapting it to ArrayList instead of a HashMap but doesn't work...

static Map sortByValue(Map map) {
     List list = new LinkedList(map.entrySet());
     Collections.sort(list, new Comparator() {
          public int compare(Object o1, Object o2) {
               return ((Comparable) ((Map.Entry) (o1)).getValue())
              .compareTo(((Map.Entry) (o2)).getValue());
          }
     });

Map result = new LinkedHashMap();
for (Iterator it = list.iterator(); it.hasNext();) {
     Map.Entry entry = (Map.Entry)it.next();
     result.put(entry.getKey(), entry.getValue());
     }
return result;
}

The values of this 3rd field are not all distinct (i.e. 2 rows can have the same int value)

Does anybody have an idea ?

Thanks in advance!

[r035198x]

You don't need a Map for this.
Create a class (say called Record) that represents the data with those fields field1, field2, etc as properties and then simply load the records into a List<Record>. You then Collections.sort the list passing a Comparator that compares the 3rd field values of a Record.

[ze snow]

Ok I kind of see but do you have an example (i mean some code) to illustrate ? I'm still not that familiar with that comparator and it seems I have to override the method compare ?

Thanks

[r035198x]

Generic heap sort algorithm A - Java insights

[camickr]

You can use a Column Comparator or Bean Comparator, depending on how you decide to store each row of data from the file.

[ze snow]

Thanks both for your help!

I chose to follow the link posted by r035198x, so I created another class and overrid the compare method inside and yes, that works!