Sorting in Java
Author
I'm pretty new to Java, and have come across the following problem :
I have a two dimensionnal array that I want to sort on one column (parameters: (column, asc). What's the easiest way to achieve this ? I need to get the other columns to follow and that's what's got me stumped.
Are there sorting algorithms already implemented that will allow me to do this ? I'd rather not rewrite a quicksort for a variable number of column and content, and I need something rather fast.
I sort Strings, numbers and Dates. The ability to plug my own comparison functions would be a plus.
Note that for compatibility reasons, I have to use JDK 1.4, and hence can't use the features introduced since 1.5.
I think you could make this easier if you encapsulate each row into an object.
You say you have Strings, numbers, and Dates. So let's make a class called DoHickey that is composed of those things.
Then you make a 1-D array of DoHickey objects which is an array of "rows" and sort it.
Of course, the DoHickey class does make it so you need to cast from Object when retrieving objects from the cols[] array, or you could add getter methods for each element if there aren't too many.
You say you have Strings, numbers, and Dates. So let's make a class called DoHickey that is composed of those things.
public class DoHickey implements Comparable { // these are your columns public Object[] cols; private int sortParam; // this will tell us which "column" to sort public DoHickey(String s, int n, float f, Date d) { cols = new Obj[4]; cols[0] = s; cols[1] = new Integer(n); // have to create an object from the primitive type cols[2] = new Float(f); // which comes in handy when we are going to sort cols[3] = d; } // set the parameter to sort on // (do a check here to make sure s is a valid column number) public void setSortParam(int s) { sortParam = s; } // In order to sort DoHickey objects you need to implement Comparable // which is just the compareTo() method public int compareTo(Object o) { DoHickey dh = (DoHickey) o; return cols[sortParam].compareTo(dh.cols[sortParam]); // this works out nice because String, Integer, Float, and Date all implement the Comparable interface }}Then you make a 1-D array of DoHickey objects which is an array of "rows" and sort it.
DoHickey[] dharray;// initialize it somewhereArrays.sort(dharray); // Arrays.sort will sort anything that implements ComparableOf course, the DoHickey class does make it so you need to cast from Object when retrieving objects from the cols[] array, or you could add getter methods for each element if there aren't too many.
Author
Yeah, I didn't want to resort to encapsulating each rows in an object since there are thousands of combinations of columns for each row set, and that meant a major rework of the class hierarchy but I did it and the code is much cleaner now.
Works like a charm.
Thanks a bunch.
Works like a charm.
Thanks a bunch.
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