Best structure for list of key-value (integer, string) to be shuffled

Question

I need to implement a structure in Java that is a key-value list (of types Integer-String) and I want to shuffle it.

Basically, I would like to do something like that.

    public LinkedHashMap<Integer, String> getQuestionOptionsMap(){

    LinkedHashMap<Integer, String>  shuffle = new LinkedHashMap<Integer, String> ();

    if (answer1 != null)
        shuffle.put(new Integer(1), answer1);
    if (answer2 != null)
        shuffle.put(new Integer(2), answer2);
    if (answer3 != null)
        shuffle.put(new Integer(3), answer3);
    if (answer4 != null) 
        shuffle.put(new Integer(4), answer4);

    Collections.shuffle(shuffle);
    return shuffle;
}

However, HashMap cannot be shuffled.

I could randomly get a key from the hashmap, and then return the linked element, but I'm sure this is not the best solution for my problem.

Is there any better way?

Thanks in advance.

DO you want the integer as a key or String as the key as you have it both ways in the code. You need a List if you want to shuffle. — Peter Lawrey, Sep 13 '13 at 08:53
Sorry my fault, I corrected my code above. Key is the integer, value is the string (the text of my answer). — MDT, Sep 13 '13 at 08:56
please check http://stackoverflow.com/questions/5289222/how-to-shuffle-key-value-pairs — upog, Sep 13 '13 at 08:58
Thanks I saw that thread, but I don't want to modify keys and values. I just want to get a pair (key-value) randomly. — MDT, Sep 13 '13 at 09:03

score 15 · Accepted Answer · answered Sep 13 '13 at 08:57

15

Create a Pair class, that holds both the Integer and the String and then add multiple Pair objects to a List, which will be shuffled.

public class Pair {
  private Integer integer;

  private String string;

  //accessors
}

Then:

List<Pair> list = new ArrayList<Pair>();
//...add some Pair objects to the list
Collections.shuffle(list);

answered Sep 13 '13 at 08:57

Konstantin Yovkov

62,134
8
100
147

7

Then you won't get HashMap's O(1) lookup though. – Kayaman Sep 13 '13 at 08:58
Thanks, I chose this solution, implementing my Pair class as a class inside my main Class. – MDT Sep 13 '13 at 10:22

Peter Lawrey · Answer 2 · 2013-09-13T09:02:34.007

You can keep the Map. The Map is designed to be looked up by key so I suggest you have a list of shuffled keys.

public Map<Integer, String> getQuestionOptionsMap() {
    Map<Integer, String> map = new HashMap<>();
    String[] answers = {null, answer1, answer2, answer3, answer4};
    for (int i = 1; i < answers.length; i++)
        if (answers[i] != null)
            map.put(i, answers[i]);
    List<Integer> order = new ArrayList<>(map.keySet());
    Collections.shuffle(order);
    Map<Integer, String> shuffled = new LinkedHashMap<>();
    for (Integer key : order)
        shuffled.put(key, map.get(key));
    return shuffled;
}

Kayaman · Answer 3 · 2013-09-13T09:00:00.227

2

You could keep a separate List of the keyvalues, shuffle that and use it to access the HashMap.

List<Integer> keys = new ArrayList<Integer>(map.keySet());
Collections.shuffle(keys);
for(Integer i : keys)
    map.get(i);     // Gets the values in the shuffled order

edited Sep 13 '13 at 09:00

answered Sep 13 '13 at 08:53

Kayaman

72,141
5
83
121

Yes that's what I wrote at the end of my question, but I wasn't sure was the best option. Thanks. – MDT Sep 13 '13 at 10:22

Oleg Mikhailov · Answer 4 · 2019-06-25T09:32:35.433

0

Hashtable<Integer, String>

As an alternative to less convenient and effective List<SomePairClass<Integer, String>>

edited Jun 25 '19 at 09:32

answered Jun 25 '19 at 08:37

Oleg Mikhailov

5,751
4
46
54

1

Maybe a few explanations would be useful? – olinox14 Jun 25 '19 at 09:16

score 0 · Answer 5 · answered Jul 04 '20 at 18:33

You can use enum to achieve this, example

package device.packet.data;

public enum TLVList {
    
    SpeedingAlarm(0x1001, 3, Short.class),
    LowVoltageAlarm(0x1002, 3, Short.class),
    OBDCommunicationError(0x1015, 3, Short.class),
    IgnitionOn(0x1016, 3, Short.class),
    IgnitionOff(0x1017, 3, Short.class),
    MILAlarm(0x1018, 3, Short.class),
    UnlockAlarm(0x1019, 3, Short.class),
    NoCardPresented(0x101A, 3, Short.class),
    HiddenCommand(0x101B, 3, Short.class),
    Vibration(0x101C, 3, Short.class),
    DoorOpened(0x101D, 3, Short.class);
    
    private int tagFlagHex;
    private int length;
    private Class aClass;

    public int gettagFlagHex() {
        return tagFlagHex;
    }

    public int getLength() {
        return length;
    }

    public Class getClassType() {
        return aClass;
    }

    TLVList(int tagFlagHex, int length, Class aClass) {

        this.tagFlagHex = tagFlagHex;
        this.length = length;
        this.aClass = aClass;
    }

    public static TLVList of(Integer tagFlagHex) {
        for (TLVList tagFlag : TLVList.values()) {
            if(tagFlag.tagFlagHex == tagFlagHex) return tagFlag;
        }
        return null;
    }
}

I hope it helps.

Best structure for list of key-value (integer, string) to be shuffled

5 Answers5

Linked