Android, create one arraylist from two arraylists

Question

I have a problem with comparing two arraylist,

my first arraylist looks like this:

{TeamID=4, Group=A, TeamName=Germany}
{TeamID=6, Group=A, TeamName=Turkey}

my second list:

{TeamID=4, Chance=99.9%}
{TeamID=6, Chance=38.4%}

and then I want to create one list, which will look like this:

{TeamID=4, Group=A, TeamName=Germany Chance=99.9%}
{TeamID=6, Group=A, TeamName=Turkey Chance=38.4%}

Can You help me ?

First List:

private ArrayList<HashMap<String, String>> TeamList = this.xml.TeamListList;

Second:

private ArrayList<HashMap<String, String>> QChanceList = this.xml.QChanceListList;

looks like a SQL join using teamID as your primary key - depending on the size and nature of your data / app you may want to think about using SQLLite — Dori
– Dori, Commented Jun 9, 2011 at 11:43

Andreas Dolk · Accepted Answer · 2011-06-09 12:18:13Z

Here's one idea. For each team I search for the corresponding entry in the chances list, then I put all entries from both maps into a new one.

public static List<Map<String, String>> merge(
      List<Map<String, String>> teams, List<Map<String, String>> chances) {

  // create the result
  List<Map<String, String>> result = new ArrayList<Map<String, String>>();

  // now we assume that for each team there is one chance (valid?)
  for (Map<String, String> team:teams) {
    boolean success = false;
    Map<String, String> combined = new HashMap<String, String>();
    combined.putAll(team);

    String id = team.get("TeamID");

    // now we have to find the "chance" map
    for (Map<String, String> chance:chances) {
       if (chance.get("TeamID").equals(id)) {
          combined.putAll(chance);
          boolean success = true;
          break;
       }
    }

    if (!success) {
      // there was no entry in chances map with this id!! -> handle problem
    }
    result.add(combined);
  }
  return result;
}

(This example is not very fail-safe, it asserts, that all maps have values for "TeamId", I just demonstrate that something has to be done in case of illegal input, like an incomplete chances list)

Kaj · Accepted Answer · 2011-06-09 12:19:03Z

1

Team list should be a map of maps. Use team id as key in the outer map (if you don't want to change to a database).

Merging the entries would then be very easy. Iterate over chance list, get the team from the teams map, and use teamMap.putAll(mapFromChanceList)

Edit: Update with example.

Map<String, Map<String, String> teams = new HashMap<String, Map<String, String>();
Map<String, String> team = new Map<String, String>();
//populate the team map, and with TeamID, TeamName etc, then do something like this.
teams.put(team.get("TeamID"), team);


//You get a team by doing:
Map<String, String> team = teams.get(teamId);  //where teamId is e.g. "4"

edited Jun 9, 2011 at 12:19

answered Jun 9, 2011 at 11:52

Kaj

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3 Comments

Dawid Sajdak Over a year ago

thxfor the reply, can You tell me, how can I create map of maps with key ?

Dawid Sajdak Over a year ago

thx, I have another one question, can I put this map into ListView ?

Kaj Over a year ago

@Grins. Not in an easy way, it's better to have a parallel array with the keys, and create a ListView with that array as source.

Travis · Accepted Answer · 2011-06-09 12:33:04Z

Similarly to Andreas_D, here's another way to skin that cat.

I would like to say that I still agree with Dori, this really does look like database data. I'd recommend you use a database and save yourself the headache of solving this problem that's already been solved.

Either that or work with the owner of the API you're using to get this data and get them to use a proper database query to merge it before it ever gets to you.

Forgoing that, your best bet is to do something like this to get to that point so that you can use the utilities of hashmap.

....
HashMap<String, HashMap<String, String>> unifiedMap = new HashMap<String, HashMap<String, String>>();
for (HashMap<String, String> teamMap : teamList) {
    String teamId = teamMap.get("TeamID");
    HashMap<String, String> mapFromUnified = unifiedMap.get(teamId);
    if (mapFromUnified == null) {
        unifiedMap.put(teamId, teamMap);
    } else {
        for (String key : teamMap.keySet()) {
            // this will be a race condition, the last one in wins - good luck!
            mapFromUnified.put(key, teamMap.get(key));
        }
    }
}

for (HashMap<String, String> teamMap : chanceList) {
    String teamId = teamMap.get("TeamID");
    HashMap<String, String> mapFromUnified = unifiedMap.get(teamId);
    if (mapFromUnified == null) {
        unifiedMap.put(teamId, teamMap);
    } else {
        for (String key : teamMap.keySet()) {
            // this will be a race condition, the last one in wins - good luck!
            mapFromUnified.put(key, teamMap.get(key));
        }
    }
}
....

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