Question

I have a Map<String, Map<String, Double>> variable.
By way of example:

{user0, {Item1, 2.5, Item2, 3.5}}  
{user1, {Item1, 3.0, Item2, 2.0}}

I want to take the following output:

{Item1, {user0, 2.5, user1, 3.0}}  
{Item2, {user0, 3.5, user2, 2.0}}

I wrote the following code to do that:

for(Map.Entry<String, Map<String, Double>> entry : usersMap.entrySet()){
    for(Map.Entry<String, Double> ent : entry.getValue().entrySet()){
        people.put(entry.getKey(), ent.getValue());
        transform.put(ent.getKey(), people);
    }
}

but I take the following:

{Item1, {user0, 3.0, user1, 2.0}}  
{Item2, {user0, 3.0, user2, 2.0}}

Can you give me some help here?

Answer 1

You have to create a new map for every item

for(Map.Entry<String, Map<String, Double>> entry : usersMap.entrySet()){
    for(Map.Entry<String, Double> ent : entry.getValue().entrySet()){
        Map<String, Double> people = transform.get(ent.getKey());
        if (people == null) {
            people = new HashMap<>();
            transform.put(ent.getKey(), people);
        }
        people.put(entry.getKey(), ent.getValue());
    }
}

Otherwise, all values in transform contain the exact same map.

Also, you might want to rethink your variable names, e.g.:

entry     --> userItemValues
ent       --> itemValue
people    --> userValues
transform --> itemsMap

Seriously, it took me several attempts to get the code right because of the confusing names. But it should be correct now