How to sort a HashMap in ascending order

Question

I have the following Key : Value pairs.

A56:A64=9, A65:A73=9, A2:A8=7, A49:A55=7, A20:A26=7, A9:A19=11, A43:A48=6, A27:A42=16

I want to sort them in an ascending order. I tried using a TreeMap but a got this :

{A20:A26=7, A27:A42=16, A2:A8=7, A43:A48=6, A49:A55=7, A56:A64=9, A65:A73=9, A9:A19=11}

A2:A8=7 should be first, but it is coming third.

Please let me know how I can fix this.

you can use Collections.sort with a comparator. so you can decide how it will compare — Adem, Dec 15 '14 at 08:20
Default comparator sorts strings in *lexicographical* order. What you need is called *numerical order*. Check out the link in my previous comment if you want to implement custom comparator for hashmap — default locale, Dec 15 '14 at 08:24

score 7 · Accepted Answer · answered Dec 15 '14 at 08:20

7

TreeMap for a String key would use String lexicographical order by default (that's the natural ordering for Strings), unless you supply your own Comparator in the constructor.

A2:A8 comes after A20:A26 when using lexicographical order.

Your comparator would probably have to split the String key into 4 parts (for example, A20:A26 would be split to A, 20, A and 26) and compare each pair of parts separately, using integer comparison for the integer parts.

answered Dec 15 '14 at 08:20

Eran

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I splited the key on ":" then took the first parameter and replaced the "A", which gave me numeric value and normal TreeMap worked there.thanks – Umesh Kumar Dec 15 '14 at 09:04
@AutoMater You're welcome! – Eran Dec 15 '14 at 09:09

How to sort a HashMap in ascending order

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