I want to display the values in a HashMap. A HashMap may have duplicate values (but not duplicate keys), but I want to display a value only once.
So I should find whether the Map has duplicate values. I know we can iterate over the Map and use the return boolean of map.containsValue(value). I want to know whether any method exists to find duplicate values in map or we should I write code myself?
A simple solution would be to compare the size of your values list with your values set.
// pseudo-code
List<T> valuesList = map.values();
Set<T> valuesSet = new HashSet<T>(map.values);
// check size of both collections; if unequal, you have duplicates
Example:
Map<Object, Object> map = new HashMap<Object, Object>();
map.put(1,2);
map.put(3,4);
map.put(2,2);
map.put(5,3);
Set<Object> uniqueValues = new HashSet<Object>(map.values());
System.out.println(uniqueValues);
Output:
[2, 3, 4]
Try out this code
private boolean hasDuplicates(Map<Integer, List<String>> datamap){
boolean status = false;
Set valueset=new HashSet(datamap.values());
if(datamap.values().size()!=valueset.size()){
status=true;
}
else{
status = false;
}
return status;
}
There is no such method provided as of jdk1.6.
One simple way you can do is
Use apache commons library class's method
org.apache.commons.collections.MapUtils.invertMap(map)
and compare the size of actual map and invert map.
public static void main(String[] args) {
HashMap<String, Integer> map = new HashMap<>();
map.put("abc", 2);
map.put("def", 1);
map.put("hij", 4);
map.put("klm", 6);
map.put("nop", 2);
map.put("qrs", 2);
map.put("tuv", 6);
map.put("wxy", 8);
map.put("zab", 1);
map.put("cde", 5);
map.put("fgh", 4);
map.put("ijk", 3);
HashMap<Integer, String> duplicatMap = new HashMap<>();
Set<Entry<String, Integer>> entrySet = map.entrySet();
Iterator<Entry<String, Integer>> iterator = entrySet.iterator();
while(iterator.hasNext()) {
Entry<String, Integer> entry = iterator.next();
String key = entry.getKey();
Integer value = entry.getValue();
if(duplicatMap.containsKey(value)) {
duplicatMap.put(value, duplicatMap.get(value)+", "+key);
} else {
duplicatMap.put(value, key);
}
}
System.out.println(duplicatMap);
}
outPut: - {1=def, zab, 2=abc, qrs, nop, 3=ijk, 4=fgh, hij, 5=cde, 6=tuv, klm, 8=wxy} if you want to modify then use again EntrySet.
try this code but this is not optimize code :
public class HashMapDulicate {
public static void main(String[] args) {
Map<String,Integer> map=new HashMap<>();
map.put("A", 1);
map.put("B", 1);
map.put("C", 3);
map.put("D", 4);
Set set=new HashSet<>();
List list=new ArrayList<>();
for(Entry<String, Integer> mapVal:map.entrySet()) {
if(!set.add(mapVal.getValue())) {
list.add(mapVal.getValue());
}else {
set.add(mapVal.getValue());
}
}
for(Entry<String, Integer> mapVal:map.entrySet()) {
if(list.contains(mapVal.getValue())){
System.out.println(mapVal.getKey() +":" + mapVal.getValue());
}
}
}
}
Map<Integer,Person> personMap01 = new HashMap<>();
personMap01.put(1,new Person(101,"Ram","Kumar"));
personMap01.put(2,new Person(103,"Raj","Kumar"));
personMap01.put(3,new Person(101,"Ravi","Ram"));
personMap01.put(4,new Person(105,"Gopi","Nath"));
personMap01.put(5,new Person(104,"Yogesh","Waran"));
personMap01.entrySet().stream().
filter(removeDuplicate(personMap01.values())).
forEach(System.out::println);
public static Predicate<Map.Entry<Integer,Person>>
removeDuplicate(Collection<Person> personCollection){
return e->Collections.frequency(personCollection,e.getValue())==1;
}
In my one of interview interviewer Asked me to print duplicate without Set, Map and distinct in stream =
List<String> distinctElementList = new ArrayList<>();
List<Integer> numberList = Arrays.asList(1, 2, 3, 4, 4, 4, 5, 5, 6);
numberList.stream().forEach(number -> {
if (distinctElementList.stream().anyMatch(numberStr -> numberStr.contains(String.valueOf(number)))) {
String existStr = distinctElementList.stream().filter(numberStr -> numberStr.contains(String.valueOf(number))).findFirst().orElse("");
Integer index = distinctElementList.indexOf(existStr);
if (existStr.split("[|]").length == 2) {
distinctElementList.set(index, number + "|" + (Integer.valueOf(existStr.split("[|]")[1]) + 1));
}
} else {
distinctElementList.add(number + "|" + 1);
}
});
distinctElementList.stream().filter(numberStr -> !numberStr.contains(String.valueOf(1))).forEach(
numberStr -> {
String keyValueArr[] = numberStr.split("[|]");
System.out.println("Number : " + keyValueArr[0] + "--------------Count : "+keyValueArr[1]);
}
);
System.out.println("Original List : " + numberList);
System.out.println("distinctElementList List : " + distinctElementList);
