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# Sorting arrays

Posted on 2003-11-17
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I have an multidimensional array of Strings that I need to sort.  What is the fastest sorting algorithm that I can use to sort based on one column and what is the code?
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Question by:sre23
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LVL 86

Expert Comment

ID: 9766523
The one in the API. Collections.sort(List l, Comparator c)
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Author Comment

ID: 9766595
ok, well in that case my question gets a little more complex.  I was hoping to just find a few methods that would do it and adjust them to fit my needs.  What I actually have is a DefaultTableModel with 10 columns and I need to sort this table on alphabetically on the 3rd column.  I looked in the API but I am a little confused on how to create a Comparator and List object.  Can you elaborate on that a little.  I've raised the points to 100 since my question has changed a little.
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Accepted Solution

CEHJ earned 400 total points
ID: 9767061
class MyTableModel extends DefaultTableModel implements Comparator {

int sortColumn;

public void sortColumn(int sortColumn) {
this.sortColumn = sortColumn;
Collections.sort(dataVector,this);
}

public int compare(Object o1, Object o2)  {
if (o1 == null) return -1;
if (o2 == null) return 1;

Vector vect1 = (Vector) o1;
Vector vect2 = (Vector) o2;
Comparable col1 = (Comparable) vect1.get(sortColumn);
Comparable col2 = (Comparable) vect2.get(sortColumn);
return col1.compareTo(col2);
}

}
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LVL 2

Expert Comment

ID: 9767185
Here is code that will do it.  You have to worry about making sure table is not updated while sorting, handling class cast and null, if there is a chance of that happening.  For regular alphabetic sorting, you do not need a comparator.  Post if you need a sample comparator.

javax.swing.table.DefaultTableModel table = new javax.swing.table.DefaultTableModel(10,10);

table.setValueAt("rasldkfj",0,2);
table.setValueAt("wqerpoiu",1,2);
table.setValueAt("nevernul",2,2);
table.setValueAt("aslgfwpo",3,2);
table.setValueAt("zasdflks",4,2);
table.setValueAt("bajklsdf",5,2);
table.setValueAt("oqpwiuir",6,2);
table.setValueAt("Zasdflk9",8,2);
table.setValueAt("8slagjwi",9,2);

//create array
int ln = table.getRowCount();
String[] test = new String[ln];

for (int i=0;i<ln;i++) {
if (table.getValueAt(i,2) == null)
test[i]="";
else test[i]=(String)table.getValueAt(i,2);
}

java.util.Arrays.sort(test);  // no comparator required for String, built-in alphabetic comparator.
// can use non-casesensitive comparator etc.

// lets see
for (int i=0;i<test.length; i++) System.out.println(test[i]);

// good, set it

for (int i=0;i<test.length; i++) table.setValueAt(test[i],i,2);
0

LVL 1

Author Comment

ID: 9767301
CEHJ, in your example how is the sort started? and what is dataVector?  And I assume that "this" can be replaced by the name of my DefaultTableModel?
0

LVL 1

Author Comment

ID: 9767321
dyanet, your example looks as though it just sorts the 3rd column.  I need to sort my entire table ON the 3rd column.  I can't just reorder one column otherwise the whole table will be changed.  Each row needs to stay intact.
0

LVL 86

Expert Comment

ID: 9767357
dataVector is a protected field of DTM:

http://java.sun.com/j2se/1.4.2/docs/api/javax/swing/table/DefaultTableModel.html#dataVector

>>how is the sort started?

By calling sortColumn on the model. Just merge the code with your model
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Author Comment

ID: 9774312
Thanks again CEHJ
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LVL 86

Expert Comment

ID: 9774827
:-)
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