Get map key based on index

Question

I want to get a LinkedHashMap key based on index. I have tried this and used a LinkedHashMap implementation instead of HashMap implementation to preserve order of insertion.

I have used below code (from some SO post I can't seem to find) to get Key By Value :

private Long getKeyByValue(Map<Long, String> map, String value) {

    for (Map.Entry<Long, String> entry : map.entrySet()) {
        if (entry.getValue().equalsIgnoreCase(value)) {
            return entry.getKey();
        }
    }

    // -1 if key not found
    return (long) -1;
}

The problem is, above method is useful only when Map value is not custom or not a collection. In my case, I have a Map<String, List<Issues>> where Issues is my own defined class and I want to get, say, 2nd key which is String based on index which is 2, in this case. Suggestions?

You need to implement an inner for loop and iterate over the `issues` collection if found Hashmap key can be returned — Murtaza Khursheed Hussain, Sep 26 '16 at 11:22

Mike Nakis · Answer 1 · 2016-09-26T15:10:47.267

2

how about this:

static <K> K getKeyByIndex( Map<K,?> sortedMap, int index )
{
    assert index >= 0;
    assert index < sortedMap.size();
    for( K key : sortedMap.keySet() )
    {
        if( index == 0 )
            return key;
        index--;
    }
    assert false; //should never happen.
}

edited Sep 26 '16 at 15:10

answered Sep 26 '16 at 11:32

Mike Nakis

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Get map key based on index

1 Answers1