android arraylist get hashmap position

Question

I have an ArrayList HashMap like the one below.

    ArrayList<HashMap<String, String>> mArrType = new ArrayList<>();

with the following values added into it

    HashMap<String, String> map;

    map = new HashMap<String, String>();
    map.put("type", "TRIMMER");
    map.put("request", "5");
    map.put("actual", "0");
    mArrType.add(map);

    map = new HashMap<String, String>();
    map.put("type", "HAND ROUTER");
    map.put("request", "6");
    map.put("actual", "0");
    mArrType.add(map);

    map = new HashMap<String, String>();
    map.put("type", "AIR COMPRESSOR");
    map.put("request", "6");
    map.put("actual", "0");
    mArrType.add(map);

Question is how can i get the position of a hashmap from arraylist. eg : hashmap with 'type' trimmer has a position 0 in arraylist, I want to retrieve the position value "0"

Of course, what you really should be doing here is creating a class Equipment. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Oct 7, 2016 at 5:17

Suresh Atta · Accepted Answer · 2016-10-07 03:59:10Z

2

I'll write a small util method

private static int getTrimmerTypeMapPosition(ArrayList<HashMap<String, String>> mArrType) {
        for (int i = 0; i < mArrType.size(); i++) {
            HashMap<String, String> mp = mArrType.get(i);
            if (mp.get("type").equals("TRIMMER")) {
                return i;
            }    
        }    
        return -1;    
    }

To make this method very generic, have "type" and "TRIMMER" as method params, so that you can just pass any key and value pairs to check with.

edited Oct 7, 2016 at 3:59

answered Oct 7, 2016 at 3:50

Suresh Atta

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2 Comments

Roman_D Over a year ago

I suppose better to check like this "TRIMMER".equals(mp.get("type")) to prevent exception in case when mp.get("type") returns null.

Suresh Atta Over a year ago

@Roman_D I'll leave that decisions to OP as he will check what if type is not present in map at all.:)

Œlrim · Accepted Answer · 2016-10-07 03:54:01Z

0

That's not efficiently possible with your data structure. You can either store the own position in each HashMap or loop through all entries and search for the one with the type you are looking for.

You can, of course, define another HashMap<String, Integer> which maps all your type strings to the corresponding ArrayList index.

answered Oct 7, 2016 at 3:54

Œlrim

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3 Comments

Suresh Atta Over a year ago

I dont think OP need extra map. Just iterate over list and look up for type ?

Œlrim Over a year ago

Yes, but if he has very many entries in the ArrayList it's more efficient to hash it.

Aaron Over a year ago

You have a point, I've tried store position value in each hashmap and it works. But I marked suresh answer as the best, cheers.

Sachin Gupta · Accepted Answer · 2016-10-07 04:17:05Z

0

Others answer is also correct, but you can do this thing using Java8 also.

E.g.:

int index = IntStream.range(0, mArrType.size()).
                filter(i -> mArrType.get(i).get("type").equals("TRIMMER"))
                .findFirst().getAsInt();

edited Oct 7, 2016 at 4:17

answered Oct 7, 2016 at 3:55

Sachin Gupta

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2 Comments

Suresh Atta Over a year ago

Not just map, needed index of map which have a "type" value "Trimmer"

Sachin Gupta Over a year ago

Yes he is, thank for pointing this thing. i have updated my answer accordingly.

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