How to remove null { } map from ArrayList<HashMap<String, String>>?

Question

I have a ArrayList<HashMap<String, String>> placesListItems.

When I remove a map from placesListItems, the null map remains. So that my ListAdapter contains null list items.

for (HashMap<String, String> map : placesListItems) {
  for (Entry<String, String> entry : map.entrySet()) {
    for (int j = 0; j < duplicateList.size(); j++) {
      if (entry.getValue().equals(duplicateList.get(j))) {
        Iterator iterator = map.entrySet().iterator();
        while (iterator.hasNext()) {
          Entry<String, String> pairs = (Entry)iterator.next();
          System.out.println(pairs.getKey() + " = " + pairs.getValue());
          iterator.remove(); // avoids a ConcurrentModificationException
        }
      }
    }
  }
}     
ListAdapter adapter = new ItemAdapterHome(getApplicationContext, placesListItems);
lv.setAdapter(adapter);

How can I solve this?

you are never removing anything from the placesListItems List. — njzk2
– njzk2, Commented May 16, 2013 at 8:23

Kshitij · Accepted Answer · 2013-05-16 08:36:24Z

What you need to do is add all empty maps in list and remove them all at the end.

List<HashMap<String, String>> mapsToRemove= new ArrayList<HashMap<String, String>>();//list in which maps to be removed will be added
for (HashMap<String, String> map : placesListItems)
   {
    for (Entry<String, String> entry : map.entrySet())
     {
      for (int j = 0; j < duplicateList.size(); j++) 
          {
        if(entry.getValue().equals(duplicateList.get(j)))
         {
          Iterator iterator = map.entrySet().iterator();
          while (iterator.hasNext()) 
               {
              Entry<String, String> pairs = (Entry)iterator.next();
              System.out.println(pairs.getKey() + " = " + pairs.getValue());
              iterator.remove(); // avoids a ConcurrentModificationException                   }
               }
          }
      }
      if(map.isEmpty){//after all above processing, check if map is empty
         mapsToRemove.add(map);//add map to be removed
      }
 }  
placesListItems.removeAll(mapsToRemove);//remove all empty maps


ListAdapter adapter = new ItemAdapterHome(getApplicationContext, placesListItems);
lv.setAdapter(adapter);

You might need to change the logic a little based on your requirement.

Étienne Miret · Accepted Answer · 2013-05-16 08:45:31Z

2

Your problem is that you are emptying maps instead of removing them from the list.

Try the following:

Iterator<Map<String, String>> iterator = placesListItems.iterator();
while (iterator.hasNext()) {
    Map<String, String> map = iterator.next();
    for (String value : map.values()) {
        if (duplicateList.contains(value)) { // You can iterate over duplicateList, but List.contains() is a nice shorthand.
            iterator.remove(); // Removing the map from placesListItems
            break; // There is no point iterating over other values of map
        }
    }
}

answered May 16, 2013 at 8:45

Étienne Miret

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