Erik Hatcher <erik <at> ehatchersolutions.com> writes:
> Lucene's index works with any String. But, when dealing with numbers
> and dates such that range queries work, they need to be formatted in a
> way that makes them orderable.
What I am suggesting here is storing numeric values as unsigned binary values so
that they can be used in a range query. To convert a signed 2's complement
number to an unsigned number you just flip the left most bit. The easiest way
to do this is to add the min value (eg Integer.MIN_VALUE).
Then to convert the integer to chars I would do somehing like this:
int unsigned = signed + Integer.MIN_VALUE;
char c2 = (char) (unsigned & 0x0000FFFF);
char c1 = (char) (unsigned >> 16 & 0x0000FFFF);
String intText new String(new char[] {c1, c2});
As I don't often think in binary I wrote a little test to verify that this is
correct according to String.compareTo() which is used during index creation to
sort the fields.
public class NumberCompareTest
{
public static String convertTotText(int input)
{
int unsigned = input + Integer.MIN_VALUE;
char c2 = (char) (unsigned & 0x0000FFFF);
char c1 = (char) (unsigned >> 16 & 0x0000FFFF);
return new String(new char[] {c1, c2});
}
public static void main(String[] args)
{
isLessThan(convertTotText(-1), convertTotText(0));
isLessThan(convertTotText(0), convertTotText(1));
isLessThan(convertTotText(Integer.MIN_VALUE), convertTotText(0));
isLessThan(convertTotText(Integer.MIN_VALUE),
convertTotText(Integer.MAX_VALUE));
isLessThan(convertTotText(0), convertTotText(Integer.MAX_VALUE));
// will be false
isLessThan(convertTotText(45), convertTotText(21));
}
public static void isLessThan(String s1, String s2)
{
System.out.println(s1.compareTo(s2) < 0);
}
}
It all seems to work OK so will this also work for Lucene? Possibly Field.java
could be have a isNumeric field added to it.
John
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