Alphanumeric sorting of ArrayList with HashMap

Question

I have an ArrayList with several objects per index. I want to sort this list alphanumerically by one object in particular. The object is "my_id" and the values for this object can look similar to: 1A, 10B, 11B, 2C, 205Z, etc.

I need to sort these to come out: 1A, 2C, 10B, 11B, 205Z. Where the numeric part is sorted first, then the alpha- part is sorted secondary. 1,2,3,4,5,... A,B,C,D,E,...

I checked out some alphanumeric string sorting that worked really well: http://sanjaal.com/java/206/java-data-structure/alphanumeric-string-sorting-in-java-implementation/

Unfortunately I can only get that object to sort and I lose the other objects in my ArrayList as a consequence. I really need a sorting algorithm that can rearrange the ArrayList index's by the object of my choosing and not lose the other objects!

Is there a method to do this already out there? I've been unable to find one. I think it's useful to add that all the objects in my ArrayList are mapped strings: ArrayList<HashMap<String, String>>

[edit] I have my array: ArrayList<HashMap<String, String>> al

I then store the object:

String[] alphaNumericStringArray = new String[al.size()];
        for(int i = 0; i < al.size(); i++)
        {
            alphaNumericStringArray[i] = al.get(i).get("my_id");
        }

I now sort the string array:

// Sort the array now.
        Arrays.sort(alphaNumericStringArray, new AlphanumericSorting());

I then put the object back:

for(int i = 0; i < al.size(); i++)
        {
            HashMap<String, String> map = new HashMap<String, String>();
                map.put("my_id", alphaNumericStringArray[i]);
                // TODO, need to append the rest of the objects.
            al.set(i, map);
        }

I know what you're thinking, I'm not adding all the objects BACK when I re-map it. This is what I have currently, but what I want is a way to sort the whole list not just the one object "my_id". I want to rearrange the indexes so I don't have to re-map everything at the end.

Why do you lose objects? I do not see how you can lose objects by sorting a list? — Deutro
– Deutro, Commented Feb 26, 2015 at 15:38
"ArrayList with several objects per index", elaborate this... — waqaslam
– waqaslam, Commented Feb 26, 2015 at 15:41
could you post your code? maybe you're doing the sorting right but you're not saving your objects. — Uriel Arvizu
– Uriel Arvizu, Commented Feb 26, 2015 at 15:42
@UrielArvizu That is what I have in mind, but he failed to mention this important clue anywhere. However, it's still our assumption. :) — waqaslam
– waqaslam, Commented Feb 26, 2015 at 15:44

Boris Pavlović · Accepted Answer · 2015-02-26 15:52:43Z

2

Running the main method:

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

public class Sorter {

    public static void main(String[] args) {

        List<String> unsorted = Arrays.asList("1A", "10B", "B", "753c", "Z", "M7", "32x", "11B", "2C", "205Z");

        Collections.sort(unsorted, new Comparator<String>() {

            @Override
            public int compare(String o1, String o2) {

                if (o1.isEmpty())
                    return -1;

                if (o2.isEmpty())
                    return 1;

                String o1number = extractNumberPrefix(o1);

                String o2number = extractNumberPrefix(o2);

                if (o1number.isEmpty())
                    if (o2number.isEmpty())
                        return o1.compareTo(o2);
                    else return 1;

                if (o2number.isEmpty())
                    return -1;

                if (o1number.equals(o2number))
                    return o1.compareTo(o2);

                return Integer.parseInt(o1number) - Integer.parseInt(o2number);
            }

            private String extractNumberPrefix(String o1) {

                String result = "";
                for (int i = 0; i < o1.length(); i++) {
                    try {
                        Integer.parseInt(o1.substring(i, i + 1));
                        result += o1.substring(i, i + 1);
                    } catch (Exception e) {
                        break;
                    }
                }
                return result;
            }
        });

        System.out.println("sorted = " + unsorted);
    }
}

returns:

sorted = [1A, 2C, 10B, 11B, 32x, 205Z, 753c, B, M7, Z]

answered Feb 26, 2015 at 15:52

Boris Pavlović

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2 Comments

Brandon Over a year ago

I have the alphanumeric sorting down with a string array String[] but what I need is an ArrayList with mapped objects to sort based off an object of my choosing, i.e., "my_id" ex: al.get(i).get("my_id") <--

OldCurmudgeon Over a year ago

OP wants to sort HashMaps, by the value behind one key. The rest you seem to have correct.

Brandon · Accepted Answer · 2015-02-26 16:56:45Z

After careful reconstruction of the Comparator and all the comments I finally figured out how to do this.

Question: To reiterate what my goal is, as well as the solution. I have an ArrayList<HashMap<String, String>>. I want to sort the ArrayList by one object in the HashMap. My HashMap has more than 1 object in it so I want to retain the entire index of the Array. I also want to sort alphanumerically where numeric values are the first to be sorted, than I sort alphabetically. i.e., 1,2,3,4,... A,B,C,D,...

References: http://sanjaal.com/java/206/java-data-structure/alphanumeric-string-sorting-in-java-implementation/

TL;DR Solution: In my custom Comparator function public int compare(object firstObj, Object secondObj) I needed to change the String values to HashMap object references/values. Here the KEY_ID is the object that I wanted to sort by. Once I did this I used Collections.sort to sort by the HashMap comparator rather than the Arrays.sort (Collections handles ArrayList/HashMaps).

Code Solution:

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;

/** 
 * DOCUMENTATION: 
 * http://sanjaal.com/java/206/java-data-structure/alphanumeric-string-sorting-in-java-implementation/ 
 **/

@SuppressWarnings({"rawtypes", "unchecked"})
public class AlphanumericSorting implements Comparator 
{
    public int compare(Object firstObjToCompare, Object secondObjToCompare) 
    {
        String firstString  = ((HashMap<String,String>) firstObjToCompare).get("KEY_ID");
        String secondString = ((HashMap<String,String>) secondObjToCompare).get("KEY_ID");

        //String firstString    = firstObjToCompare.toString();
        //String secondString = secondObjToCompare.toString();

        if (secondString == null || firstString == null) 
        {
            return 0;
        }

        int lengthFirstStr  = firstString.length();
        int lengthSecondStr = secondString.length();

        int index1 = 0;
        int index2 = 0;

        while(index1 < lengthFirstStr && index2 < lengthSecondStr) 
        {
            char ch1 = firstString.charAt(index1);
            char ch2 = secondString.charAt(index2);

            char[] space1 = new char[lengthFirstStr];
            char[] space2 = new char[lengthSecondStr];

            int loc1 = 0;
            int loc2 = 0;

            do 
            {
                space1[loc1++] = ch1;
                index1++;

                if (index1 < lengthFirstStr) 
                {
                    ch1 = firstString.charAt(index1);
                } 
                else 
                {
                    break;
                }
            } 
            while (Character.isDigit(ch1) == Character.isDigit(space1[0]));

            do 
            {
                space2[loc2++] = ch2;
                index2++;

                if (index2 < lengthSecondStr) 
                {
                    ch2 = secondString.charAt(index2);
                } else 
                {
                    break;
                }
            } 
            while (Character.isDigit(ch2) == Character.isDigit(space2[0]));

            String str1 = new String(space1);
            String str2 = new String(space2);

            int result;

            if (Character.isDigit(space1[0]) && Character.isDigit(space2[0])) 
            {
                Integer firstNumberToCompare    = new Integer(Integer.parseInt(str1.trim()));
                Integer secondNumberToCompare   = new Integer(Integer.parseInt(str2.trim()));

                result = firstNumberToCompare.compareTo(secondNumberToCompare);
            } 
            else 
            {
                result = str1.compareTo(str2);
            }

            if (result != 0) 
            {
                return result;
            }
        }

        return lengthFirstStr - lengthSecondStr;
    }

    /**
     * ALPHANUMERIC SORTING
     */
    public static ArrayList<HashMap<String, String>> sortArrayList(ArrayList<HashMap<String, String>> al)
    {
        Collections.sort(al, new AlphanumericSorting());

        return al;
    }
}

To return the sorted ArrayList:

myArrayList = AlphanumericSorting.sortArrayList(myArrayList);

Where,

ArrayList<HashMap<String, String>> myArrayList;

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