I have problem with default comparator for Strings (in SortedSet). The problem is that default comparator doesn't sort good String that contains numbers i.e.: In set i have:
room1, room2, room100
Natural ordering should be like above but in set I have:
room1, room100, room2
I know why it is but I don't know how to change it.
Try this comparator, which removes all non-digit characters then compares the remaining characters as numbers:
Collections.sort(strings, new Comparator<String>() {
public int compare(String o1, String o2) {
return extractInt(o1) - extractInt(o2);
}
int extractInt(String s) {
String num = s.replaceAll("\\D", "");
// return 0 if no digits found
return num.isEmpty() ? 0 : Integer.parseInt(num);
}
});
When this code is run:
public static void main(String[] args) {
List<String> strings = Arrays.asList("room1.2", "foo1.1", "foo", "room2.3", "room100.999", "room10", "room.3");
Collections.sort(strings, new Comparator<String>() {
public int compare(String o1, String o2) {
return extractInt(o1) - extractInt(o2);
}
int extractInt(String s) {
String num = s.replaceAll("\\D", "");
// return 0 if no digits found
return num.isEmpty() ? 0 : Integer.parseInt(num);
}
});
System.out.println(strings);
}
This is the output:
[foo, room.3, room10, foo1.1, room1.2, room2.3, room100.999]
When the numbers are decimals, retain both digits and dots.
When this code (which shows use of a function instead of an anonymous class) is run:
public static void main(String[] args) {
List<String> strings = Arrays.asList("room1.2", "foo1.1", "room2.3", "room100.999", "room10", "room.3");
Collections.sort(strings, Comparator.comparing(Application::extractDouble));
System.out.println(strings);
}
static double extractDouble(String s) {
String num = s.replaceAll("[^\\d.]", "");
// return 0 if no digits found
return num.isEmpty() ? 0 : Double.parseDouble(num);
}
This is the output:
[room.3, foo1.1, room1.2, room2.3, room10, room100.999]
Used @bohemian answer. Just improved a bit. This worked for me very well..
Collections.sort(asdf, new Comparator<String>() {
public int compare(String o1, String o2) {
String o1StringPart = o1.replaceAll("\\d", "");
String o2StringPart = o2.replaceAll("\\d", "");
if(o1StringPart.equalsIgnoreCase(o2StringPart))
{
return extractInt(o1) - extractInt(o2);
}
return o1.compareTo(o2);
}
int extractInt(String s) {
String num = s.replaceAll("\\D", "");
// return 0 if no digits found
return num.isEmpty() ? 0 : Integer.parseInt(num);
}
});
try this. I've assumed that you will always have "room" at the start of your string.
List<String> list = Arrays.asList("room1", "room100", "room2");
Collections.sort(list, new Comparator<String>()
{
@Override
public int compare(String o1, String o2)
{
return new Integer(o1.replaceAll("room", ""))
.compareTo(new Integer(o2.replaceAll("room", "")));
}
});
Here is my Comparator implementation for such a sort:
(strings can start from any chars)
public class StringNumberComparator implements Comparator<String>{
@Override
public int compare(String o1, String o2) {
int i1 = this.getRearInt(o1);
int i2 = getLeadingInt(o2);
String s1 = getTrailingString(o1);
String s2 = getTrailingString(o2);
if(i1==i2)
return s1.compareTo(s2);
if(i1>i2)
return 1;
else if(i1<i2)
return -1;
return 0;
}
private int getRearInt(String s) {
s=s.trim();
int i=Integer.MAX_VALUE;
try {
i = Integer.parseInt(s.split("[^0-9]+")[1]);
} catch(ArrayIndexOutOfBoundsException e) {
} catch(NumberFormatException f) {
return i;
}
return i;
}
private String getTrailingString(String s) {
return s.replaceFirst("[0-9]", "");
}
}
You can implement a comparator and pass it to the set constructor. See http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Comparator.html.
If all your strings are in the form of room[number] you can strip the "room" parse the number and compare by it.
Alternatively - you can store Integers in you set and print them with "room" prefix.
A lazy alternative would be to make the String comparator work without doing anything extra (defining your own comparator). You can have that by padding with zeros the numbers within your String like this: room0001, room0002, room0100 then the default String comparator will work. You do however, need to know the maximum number value so you can adapt your padding accordingly.
