One more question about HashMap<> in Java:
I have the following
Map<String, Set<Integer>> myWordDict = new HashMap<String, Set<Integer>>();
After storing data into the variable myWordDict, I want to iterate through the HashMapValues, and add each value to a new Set variable?
When I try to do Set<Integer> newVariable = myWordDict.entrySet(), it seems the data type is incompatible.
So my question is essentially:
how to convert HashMap values or entrySet() to Set ?
Thanks
Try:
Set<Integer> newVariable = mywordDict.keySet();
or
Set<Integer> newVariable = new HashSet<Integer>(myWordDict.values());
Your declaration should be like below. It will convert your map values to Collection
Collection<Set<Integer>> newVariable = myWordDict.values();
ClassCastException.public Set<Map.Entry<K,V>> entrySet()
Returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa.
If you want iterate over the myWordDict hash map then just
for(Map.Entry<String, Set<Integer>> entry : myWordDict.entrySet())
{
Set<Integer> newVariable = entry.getValue();
}
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If you need all the values as a Set of Integers and not as a Set of Set, then you could do something like this
Set<Integer> newVariable = new HashSet<Integer>();
for (Set<Integer> set : myWordDict.values()) {
newVariable.addAll(set);
}
Or if you want them as a Set of Set, you need to do something like this
Set<Set<Integer>> newVariable = new HashSet<Set<Integer>>();
newVariable.addAll(myWordDict.values());
flatMap will help you:
myWordDict.values().stream().flatMap(Set::stream).collect(Collectors.toSet());
use myWordDict.values(), not myWordDict.entrySet(). values is a set of the map's values, whereas entrySet is a set of its mappings (it is a set of java.util.map.Entry objects, each of which describes a key and a value).
Assuming that you want to add all values from the sets in the map your approach to do it is to use addAll method:
Set<Integer> newVariable = new HashSet<Integer>();
for (Set<Integer> set : myWordDict.values()) {
newVariable.addAll(set);
}
myWordDict - if you have 10 entries, for loop will make 10 iterations.Map<Integer,String> map1 = new HashMap<Integer,String>();
map1.put(1, "Rakesh");
map1.put(2, "Amal");
map1.put(3, "Nithish");
Set<Entry<Integer,String>> set1 = map1.entrySet();
So, I came up with an iterator to iterate through the value Set
I have this data structure
Map<String, Set<Integer>> myWordDict = new HashMap<String, Set<Integer>>();
I created
Iterator mapIterator = myWordDict.entrySet().iterator();
Then just use a while() loop to add individual value to a new Set variable. I am not sure this is the most efficient way, but it works for my needs.`