Sorting an ArrayList<Hashmap<String,String> by one field

Question

In an Android application I call a web service, get json response and put that into an ArrayList of Hashmap (each identifier returned in the JSON gets a field.

My list which stores [n] items is defined as:

private ArrayList<HashMap<String, String>> customerDataList;

When I receive the data I create a new Hashmap collection like so:

HashMap<String, String> customer = new HashMap<>();

And then I simply add the values I need for example

JSONObject thisCustomer = customerArr.getJSONObject(customerIndex);

String customerName = thisCustomer.getString(TAG_CUSTOMER_NAME);
customer.put(TAG_CUSTOMER_NAME, customerName);

double location = // get location based on GPS
customer.put(TAG_LOCATION, location);    

// snip...

Then once I have populated that customer object I add it to the list:

customerDataList.add(customer);

Now, I want to sort this data by one value, the location which I set above.

Currently after I have populated customerDataList I loop through it, build an array of all the locations, sort it, and then loop over the sorted array. Inside that I loop over customerDataList and compare the outer location (the sorted values) with the inner, and build another customerDataList which is sorted.

Is there a way I can sort without needing to have 3 loops?

Edit: Mike does your solution work with doubles?

The unsorted locations are as follows

However the final list after I call your class is

I presume that is because I store them as a string?

andrewb
– andrewb

2015-01-10 17:24:08 +00:00
Commented Jan 10, 2015 at 17:24 — andrewb
– andrewb, Commented Jan 10, 2015 at 17:24

Mike Dinescu · Accepted Answer · 2015-01-10 17:00:33Z

4

If I understood the question correctly it sounds like you could use a custom comparator to sort the array list in the first place:

public class LocationComparator 
             implements Comparator<HashMap<String, String>> 
{
   @Override
   public int compare(HashMap<String, String> o1, 
                      HashMap<String, String> o2) 
   {
       return Double.compare(o1.get(TAG_LOCATION), o2.get(TAG_LOCATION));
   }
}

Collections.sort(customerDataList, new LocationComparator());

And of course, you could use an anonymous class to implement the Comparator<> interface inline.

But as an aside, why are you storing your customer entities in hash maps? It seems wasteful..

answered Jan 10, 2015 at 17:00

Mike Dinescu

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2 Comments

dramzy Over a year ago

Beat me to it. No reason to sort with nested loops, when a cleaner implementation exists.

dramzy Over a year ago

Look at the JavaDocs, the mothod takes two doubles.

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