Sort ArrayList containing numbers and letters

Question

I have an ArrayList<String> containing a list of 'Building Key' numbers.
Forgive me if this has been answered before I am struggling to find a solution by searching.

public class SortKeyNumbers {
    
    public static void main(String args[]) {
        
        ArrayList<String> keys = new ArrayList<>();
        
        keys.add("1");
        keys.add("10");
        keys.add("2");
        keys.add("3");
        keys.add("3B");
        keys.add("12");
        keys.add("12C");
        keys.add("21");
        keys.add("32");
        
        Collections.sort(keys);
        
        System.out.println(keys);
        
    }
    
}

This gives me an output of [1, 10, 12, 12C, 2, 21, 3, 32,3B]
I know that this is as expected from Collections.sort
What I need is an output of [1, 2, 3, 3B, 10, 12, 12C, 21, 32]

What I am asking is help to write the correct comparator or compareTo to achieve the desired output.

*What I am asking is help to write the correct comparator or compareTo to achieve the desired output.* - where is your attempt? Maybe we can make a suggestion on how to improve it. We don't even know the full requirements. For example, can it only contain a single character at the end or multiple characters. What comes first "12" or "12C"? — camickr, Aug 24 '20 at 03:04

score 0 · Accepted Answer · answered Aug 24 '20 at 02:48

0

You can use a comparator function which strips any non-digit characters out of the key and then parses it to an integer:

Collections.sort(keys, Comparator.comparing(s -> Integer.parseInt(s.replaceAll("[^\\d]", ""))));

Output:

[1, 2, 3, 3B, 10, 12, 12C, 21, 32]

answered Aug 24 '20 at 02:48

Nick

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Seems so easy! I tried adding "12B" after adding "12C" but it doesn't sort them alphanumerically. Is there a way to incorporate that as well? – tonkatommy Aug 24 '20 at 02:55
@tonkatommy. *Is there a way to incorporate that as well?* - write a proper Comparator and incorporate all your rules into the Comparator. – camickr Aug 24 '20 at 03:10
@tonkatommy if you first sort alphabetically (`Collections.sort(keys)`) and then use this function, those values will sort as you desire (because Java sort is stable) – Nick Aug 24 '20 at 03:11

score 0 · Answer 2 · answered Aug 24 '20 at 02:51

0

You can use ArrayList.sort and just compare only integers by removing non digits

keys.sort(Comparator.comparing(str-> Integer.valueOf(str.replaceAll("\\D+",""))));

answered Aug 24 '20 at 02:51

Ryuzaki L

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Sort ArrayList containing numbers and letters

2 Answers2