How to sort Alphanumeric String

Question

I have a problem with sorting strings which include integers. If I use the below code I get sorting like: 1some, 2some, 20some, 21some, 3some, some

However I want it

Answer 1

Here is a self-contained example on how to do this (not particularly optimized):

final Pattern p = Pattern.compile("^\\d+");
String[] examples = { 
   "1some", "2some", "20some", "21some", "3some", "some", "1abc", "abc"
};
Comparator<String> c = new Comparator<String>() {
    @Override
    public int compare(String object1, String object2) {
        Matcher m = p.matcher(object1);
        Integer number1 = null;
        if (!m.find()) {
            return object1.compareTo(object2);
        }
        else {
            Integer number2 = null;
            number1 = Integer.parseInt(m.group());
            m = p.matcher(object2);
            if (!m.find()) {
                return object1.compareTo(object2);
            }
            else {
                number2 = Integer.parseInt(m.group());
                int comparison = number1.compareTo(number2);
                if (comparison != 0) {
                    return comparison;
                }
                else {
                    return object1.compareTo(object2);
                }
            }
        }
    }
};
List<String> examplesList = new ArrayList<String>(Arrays.asList(examples));
Collections.sort(examplesList, c);
System.out.println(examplesList);

Output

[1abc, 1some, 2some, 3some, 20some, 21some, abc, some]

Explanation

• The example uses a constant Pattern to infer whether a number is in the String's starting position.
• If not present in the first String, it compares it as is to the second.
• If present indeed in the first, it checks the second.
• If not present in the second, it compares the two Strings as is, again
• If present in both, it compares the Integers instead of the whole Strings, hence resulting in a numerical comparison rather than a lexicographical one
• If the number compare identical, it goes back to lexicographic comparison of the whole Strings (thanks MihaiC for spotting this one)

Answer 2

If you have alphanumeric string array you can directly sort it by using

Arrays.sort(Array_name)

and then to print:

for(String a : Array_name)
    System.out.print(a);

Answer 3

Your solution lies in The Alphanum Algorithm and you can implement like this

Answer 4

This is a working solution is Java. If you have any suggestions on the code, please let me know on my Gist.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class FB {

    public static int comparator(String s1, String s2) {

        String[] pt1 = s1.split("((?<=[a-z])(?=[0-9]))|((?<=[0-9])(?=[a-z]))"); 
        String[] pt2 = s2.split("((?<=[a-z])(?=[0-9]))|((?<=[0-9])(?=[a-z]))"); 
//pt1 and pt2 arrays will have the string split in alphabets and numbers

        int i=0;
        if(Arrays.equals(pt1, pt2))
            return 0;
        else{
            for(i=0;i<Math.min(pt1.length, pt2.length);i++)
                if(!pt1[i].equals(pt2[i])) {
                    if(!isNumber(pt1[i],pt2[i])) {
                        if(pt1[i].compareTo(pt2[i])>0)
                            return 1;
                        else
                            return -1;
                    }
                    else {
                        int nu1 = Integer.parseInt(pt1[i]);
                        int nu2 = Integer.parseInt(pt2[i]);
                        if(nu1>nu2)
                            return 1;
                        else
                            return -1;
                    }
                }
        }

        if(pt1.length>i)
            return 1;
        else
            return -1;
    }

    private static Boolean isNumber(String n1, String n2) {
        // TODO Auto-generated method stub
        try {
            int nu1 = Integer.parseInt(n1);
            int nu2 = Integer.parseInt(n2);
            return true;
        }
        catch(Exception x) {
            return false;
        }

    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        String[] examples = {"1some", "2some", "20some", "21some", "3some", "some", "1abc", "abc"};
        List<String> values = new ArrayList<String>(Arrays.asList(examples));

        System.out.println(values);
        Comparator<String> com = (o1,o2) -> {return comparator(o1,o2);}; //lambda expression

        Collections.sort(values,com);
        System.out.println(values);
    }
}

Output:

[1some, 2some, 20some, 21some, 3some, some, 1abc, abc]
[1abc, 1some, 2some, 3some, 20some, 21some, abc, some]

Answer 5

First make an alphanumerical comparator splitting the string in String or Integer parts.

public class AlphaNumericalComparator implements Comparator<String> {
    @Override
    public int compare(String o1, String o2) {
        List<Object> parts1 = partsOf(o1);
        List<Object> parts2 = partsOf(o2);
        while (!parts1.isEmpty() && !parts2.isEmpty()) {
            Object part1 = parts1.remove(0);
            Object part2 = parts2.remove(0);
            int cmp = 0;
            if (part1 instanceof Integer && part2 instanceof Integer) {
                cmp = Integer.compare((Integer)part1, (Integer)part2);
            } else if (part1 instanceof String && part2 instanceof String) {
                cmp = ((String) part1).compareTo((String) part2);
            } else {
                cmp = part1 instanceof String ? 1 : -1; // XXXa > XXX1
            }
            if (cmp != 0) {
                return cmp;
            }
        }
        if (parts1.isEmpty() && parts2.isEmpty()) {
            return 0;
        }
        return parts1.isEmpty() ? -1 : 1;
    }

    private List<Object> partsOf(String s) {
        List<Object> parts = new LinkedList<>();
        int pos0 = 0;
        int pos = 0;
        boolean wasDigit = false;
        while (true) {
            if (pos >= s.length()
                    || Character.isDigit(s.charAt(pos)) != wasDigit) {
                if (pos > pos0) {
                    String part = s.substring(pos0, pos);
                    parts.add(wasDigit? Integer.valueOf(part) : part);
                    pos0 = pos;
                }
                if (pos >= s.length()) {
                    break;
                }
                wasDigit = !wasDigit;
            }
            ++pos;
        }
        return parts;
    }
};

Then use this comparator in your own one, in Java 8 you may simply use Comparator's static methods.

Answer 6

How to Sort String,AlphaNumeric and Numeric value in Java using Comparator

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class AlphaNumericSorting {
    public static void main(String[] args) {
        final Pattern p = Pattern.compile("^\\d+");
        String[] examples = { "CD", "DE", "0A", "0B", "0C", "12", "0K", "TA", "0D", "01", "02", "11", "AB", "MN" };
        Comparator<String> c = new Comparator<String>() {
            @Override
            public int compare(String object1, String object2) {
                Matcher m = p.matcher(object1);
                Integer number1 = null;
                if (!m.find()) {
                    Matcher m1 = p.matcher(object2);
                    if (m1.find()) {
                        return object2.compareTo(object1);
                    } else {
                        return object1.compareTo(object2);
                    }
                } else {
                    Integer number2 = null;
                    number1 = Integer.parseInt(m.group());
                    m = p.matcher(object2);
                    if (!m.find()) {
                        // return object1.compareTo(object2);
                        Matcher m1 = p.matcher(object1);
                        if (m1.find()) {
                            return object2.compareTo(object1);
                        } else {
                            return object1.compareTo(object2);
                        }
                    } else {
                        number2 = Integer.parseInt(m.group());
                        int comparison = number1.compareTo(number2);
                        if (comparison != 0) {
                            return comparison;
                        } else {
                            return object1.compareTo(object2);
                        }
                    }
                }
            }
        };
        List<String> examplesList = new ArrayList<String>(Arrays.asList(examples));
        Collections.sort(examplesList, c);
        System.out.println(examplesList);
    }
}

OUTPUT:-

[AB, CD, DE, MN, TA, 0A, 0B, 0C, 0D, 0K, 01, 02, 11, 12]