split an array list into multiple lists in java

Question

I have an array list which when populated has a key and a value I want to know if there is a way of splitting it on repeating keys for example my current data is like this:

[RoleID_123.0, UserHandel_tom, Password_12345.0, prevPassword_null, userCaption_thomas, [email protected], RoleID_124.0, UserHandel_dave, Password_ghadf, prevPassword_sdfsd, userCaption_david, [email protected], RoleID_125.0, UserHandel_trevor, Password_tre, prevPassword_null, userCaption_trev, [email protected]]

I want it to come out more like this:

[RoleID_123.0, UserHandel_tom, Password_12345.0, prevPassword_null, userCaption_thomas, [email protected]]

[RoleID_124.0, UserHandel_dave, Password_ghadf, prevPassword_sdfsd, userCaption_david, [email protected]]

[RoleID_125.0, UserHandel_trevor, Password_tre, prevPassword_null, userCaption_trev, [email protected]]

Is there a way to split it on say role id or am I going about this the wrong way?

You just have to loop through your existing list and create a new list of lists using your splitting criteria — shyam
– shyam, Commented Aug 14, 2013 at 10:51
IMHO instead of converting that list you should generate the proper list in first time. Also each of your new lists look like actually an object, which makes me think what you really want is a list of such objects. — m0skit0
– m0skit0, Commented Aug 14, 2013 at 10:52

Sheel · Accepted Answer · 2013-08-14 10:57:45Z

You can try by using HashMap

    private static class MyItemHashMap extends HashMap {  
    public Item add(Item item) {  
        get(item).add(item);  
        return item;  
    }  

    public List get(Item key) {  
        List list = (List) get(createItemKey((Item) key));  
        return list == null ? createItemEntry((Item) key) : list;  
    }  

    private List createItemEntry(Item item) {  
        List list = new ArrayList();  
        put(createItemKey(item), list);  
        return list;  
    }  

    private Object createItemKey(Item item) {  
        return item.getSplitterProperty();  
    }  
    }  

    public static void main(String[] args) {  
    MyItemHashMap itemMapped = new MyItemHashMap();  
    List items = Arrays.asList(new Object[]{new Item("A"), new Item("B"),
    new  Item("C")});  
    for (Iterator iter = items.iterator(); iter.hasNext();) {  
    Item item = (Item) iter.next();  
    itemMapped.add(item);  
     }  
     }

devrobf · Accepted Answer · 2013-08-14 10:53:18Z

1

If it is an ArrayList, there is no built-in function to split data like this; you will have to do it manually. If you know the number of consecutive fields that make a single structure, this shouldn't be too hard; something like this:

// 6 because there are 6 fields
for (int i = 0; i < arrayList.size(); i = i + 6) {
  List thisList = arrayList.subList(i, i + 5);
  // ... Now do whatever you want with thisList - it contains one structure.
}

If the number of fields can change then you'll have to do something a little more dynamic and loop through looking for a RoleID field, for example.

answered Aug 14, 2013 at 10:53

devrobf

7,2533 gold badges36 silver badges51 bronze badges

Comments

Patrick · Accepted Answer · 2013-08-14 10:56:06Z

0

I'd use a HashMap to seperate the data instead of one long ArrayList ( you shouldn't have stored the data like this in the first instance )

HashMap<String,ArrayList<String>> hm = new HashMap<String,ArrayList<String>>;

// For each list:
    ArrayList<String> arr = new ArrayList<String>;
    arr.add("each element");
    hm.put("RoleID_123.0", arr);

This way you will end up with a three dimensional structure with a key ( "RoleID..." ) pointing to its child elements.

answered Aug 14, 2013 at 10:56

Patrick

4722 silver badges8 bronze badges

Comments

Ruchira Gayan Ranaweera · Accepted Answer · 2013-08-14 10:59:41Z

0

Try this

String[] str=new String[]{"RoleID_123.0", "UserHandel_tom", "Password_12345.0", "prevPassword_null", "userCaption_thomas", "[email protected]", "RoleID_124.0", "UserHandel_dave", "Password_ghadf", "prevPassword_sdfsd", "userCaption_david", "[email protected]", "RoleID_125.0", "UserHandel_trevor", "Password_tre", "prevPassword_null", "userCaption_trev", "[email protected]"};
 List<String> list=new ArrayList<>(Arrays.asList(str));
 List<String> subList=list.subList(0,5);

You can try something similar to this

answered Aug 14, 2013 at 10:59

Ruchira Gayan Ranaweera

35.7k17 gold badges78 silver badges117 bronze badges

Comments

Groostav · Accepted Answer · 2013-08-14 11:46:31Z

If you feel like taking a Linq-ee Libraried approach, this is about as good as it gets, and it requires use of a couple delegate objects:

import static com.google.common.collect.Collections2.filter;
import static com.google.common.collect.Collections2.transform;
//...


final List<String> yourList = //...
final int RECORD_LENGTH = 6;

Collection<String> roleIdValues = filter(yourList, new Predicate<String>() {
    public boolean apply(@Nullable String input) {
        return input != null && input.startsWith("RoleID");
    }
});
Collection<Collection<String>> splitRecords = transform(roleIdValues, new Function<String, Collection<String>>() {
    @Nullable public Collection<String> apply(@Nullable String input) {
        return yourList.subList(yourList.indexOf(input), RECORD_LENGTH);
    }
});

If Oracle had delivered Java 8 on time you would be able to do this in a way more slick manor. Ironically the reason you cant was provided by the same people providing the guava library

Collectives™ on Stack Overflow

split an array list into multiple lists in java

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related