Java - Map<String, Integer> converted to Object[], how to sort

Question

I have finally gotten my code to where it works. Although it isnt the easiest to read. I am reading from a text file that has

Date/time Tip from xxx
tip    totalAmount

My code now takes the amount tipped by a person and adds them together. eg X tip 10, X tip 20, X tip 30, Y tip 200, Z tip 30, Z tip 40 and outputs

X=60
Y=200
Z=70

I did this by turning my Map< String,Integer> into an Object[] tipsPerPerson

So how would I go about sorting this Object[] tipsPerPerson into something a bit easier to read (theres over 2000 names) a bit like this

Y=200
Z=70
X=60

Here is a portion of the code that im stuck at

import java.io.BufferedReader;
import java.io.FileReader;
import java.util.HashMap;
import java.util.Map;

public class Tip {

public static void main(String[] args)
{
    int lineNumber = 1;
    Map<String, Integer> tipsByName = new HashMap<String, Integer>();
    String fileName = "C:\\Users\\David\\Desktop\\tips.txt";

    System.out.println("Reading text from file");

    try {
        FileReader inputFile = new FileReader(fileName);
        BufferedReader bufferedReader = new BufferedReader(inputFile);
        String line;
        String currentTipper = null;

        while ((line = bufferedReader.readLine()) != null) {
            if (lineNumber % 2 != 0) {
                final String tipperName = line.substring(line.indexOf("from ") + 5);
                currentTipper = tipperName;
            } else {
                final Integer tipValue = Integer.parseInt(line.substring(0, line.indexOf("\t")));
                // here we store the tip in the map. If we have a record we sum, else 
                // we store as is
                tipsByName.put(currentTipper, (tipsByName.get(currentTipper) == null ? 0 : tipsByName.get(currentTipper))
                        + tipValue);
            }

            lineNumber++;
        }
        bufferedReader.close();
       Object[] tipsName = tipsByName.entrySet().toArray();
        for (int i = 0; i < tipsByName.size(); i++) {
            System.out.println(tipsName[i]); // output the map
        }

    } catch (Exception e) {
        System.out.println("Error while reading file line by line: " + e.getMessage());
    }
   }
}

is there a specific reason to convert to Object array? you could convert to Integer array and apply sort — gaurav5430
– gaurav5430, Commented Dec 14, 2013 at 5:32
So you want to sort the map by its values, in descending order? — Bohemian
– Bohemian ♦, Commented Dec 14, 2013 at 5:44
Ascending or descending. Just so I dont have to go back and forth checking values and putting them in order — user3079061
– user3079061, Commented Dec 14, 2013 at 5:54

clstrfsck · Accepted Answer · 2013-12-14 06:45:24Z

1

Just dump the entries into a list and sort them using a Comparator:

List<Map.Entry<String, Integer>> entries = new ArrayList<Map.Entry<String, Integer>>(map.entrySet());
Collections.sort(entries, new Comparator<Map.Entry<String, Integer>>() {
    public int compare(Map.Entry<String, Integer> a, Map.Entry<String, Integer> b) {
        return Integer.compare(b.getValue(), a.getValue());
    }
});

Note that b is compared to a, rather than the other way around, to give us reverse order (largest to smallest).

All done in two lines. If you then iterate over the list, it will be in the order you wanted. Use getKey() and getValue() to print, or simply use the default toString() of the Entry:

for (Map.Entry<String, Integer> entry : entries)
    System.out.println(entry + '\n');

edited Dec 14, 2013 at 6:45

clstrfsck

14.9k5 gold badges48 silver badges62 bronze badges

answered Dec 14, 2013 at 5:55

Bohemian♦

427k103 gold badges603 silver badges750 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

Diversity Over a year ago

But hey you need a full hd screen to meet the line reqirmentes of the your definition ;-)

clstrfsck Over a year ago

List<Map.Entry<String, Integer>> entries = new ArrayList<>(map.entrySet()); is a possibility for the first line if you are using 1.7.

user3079061 Over a year ago

You are absolutely amazing Bohemian!!!! Thank you so much!!!!!! I was going crazy trying to get this to work!

user3079061 Over a year ago

May I ask where you learned Java? I have been using a book but I feel as if its not teaching me too much other than basic syntax

Bohemian Over a year ago

Thank you! <blush/>. I learned java from a friend and have used it for about 15 years. I haven't read many books about it. I learned by doing. Learn the GOF patterns, and always look for ways to use the java JDK, especially Collections. Also learn regex - it can be so powerful and useful. Always look to learn from pros - read blogs, read the better answers here and similar forums, watch youtube videos from google devs and Josh Bloch. Lastly, try to answer questions here: You might be surprised at what you don't know when you try to answer, and how much you'll learn when you answer well.

|

Diversity · Accepted Answer · 2013-12-14 05:35:05Z

An advice: use the map and d'ont make any array convertions. The map class gives you all that you need. You can iterate over the keys or over the values or over both like you do right now.

Just use the key values of your map and pass it as an argument to Collections.sort(). This works because the returned key set is of type Collection which can be passed to the Collections.sort() method.

Than it will be ordered in alphabetical order. If you want something else just pass an additonal Comparator class to the Collection.sort() or wrap your object within a customized class which implements the interface Comparable.

After that you just iterate throught you keys and invoke map.get(key) method.

Example:

Iterator<String> sortedKeys = map.keySet().iteator();
for (String key :keys) {

  sysout(key: "+key+" value : "+ map.get(key));
}

Hope it was thge answer you needed.

Elliott Frisch · Accepted Answer · 2013-12-14 05:38:22Z

0

Ouch. Don't do that! Try this instead...

// Get the Entries.
java.util.Set<Entry<String, Integer>> entrySet = tipsByName
    .entrySet();
// Make a SortedSet with a Custom Comparator.
SortedSet<Entry<String, Integer>> sortedSet = new TreeSet<Entry<String, Integer>>(
    new Comparator<Entry<String, Integer>>() {
      public int compare(
          Entry<String, Integer> o1,
          Entry<String, Integer> o2) {
        if (o1 == o2) {
          return 0;
        } else if (o1 == null) {
          return -1;
        } else if (o2 == null) {
          return 1;
        }
        return o1.getValue().compareTo(
            o2.getValue());
      }
    });
// Add the Entries to the SortedSet.
for (Entry<String, Integer> entry : entrySet) {
  sortedSet.add(entry);
}

// Iterate the sortedSet.
Iterator<Entry<String, Integer>> iter = sortedSet
    .iterator();

while (iter.hasNext()) {
  System.out.println(iter.next()); // print your sorted items.
}

edited Dec 14, 2013 at 5:38

answered Dec 14, 2013 at 5:24

Elliott Frisch

202k20 gold badges166 silver badges265 bronze badges

1 Comment

user3079061 Over a year ago

Ill post the rest of my code so you can see what it is im doing

Collectives™ on Stack Overflow

Java - Map<String, Integer> converted to Object[], how to sort

3 Answers 3

8 Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

8 Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related