I have 2 text files with data. I am reading these files with BufferReader and putting the data of one column per file in a List<String>.
I have duplicated data in each one, but I need to have unique data in the first List to confront with the duplicated data in the second List.
How can I get unique values from a List?
It can be done one one line by using an intermediate Set:
List<String> list = new ArrayList<>(new HashSet<>(list));
In java 8, use distinct() on a stream:
List<String> list = list.stream().distinct().collect(Collectors.toList());
Alternatively, don't use a List at all; just use a Set (like HashSet) from the start for the collection you only want to hold unique values.
Convert the ArrayList to a HashSet.
List<String> listWithDuplicates; // Your list containing duplicates
Set<String> setWithUniqueValues = new HashSet<>(listWithDuplicates);
If for some reason, you want to convert the set back to a list afterwards, you can, but most likely there will be no need.
List<String> listWithUniqueValues = new ArrayList<>(setWithUniqueValues);
In Java 8:
// List with duplicates
List<String> listAll = Arrays.asList("A", "A", "B", "C", "D", "D");
// filter the distinct
List<String> distinctList = listAll.stream()
.distinct()
.collect(Collectors.toList());
System.out.println(distinctList);// prints out: [A, B, C, D]
this will also work with objects, but you will probably have to adapt your equals method.
i just realize a solution may be it can be helpful for other persons. first will be populated with duplicated values from BufferReader.
ArrayList<String> first = new ArrayList<String>();
To extract Unique values i just create a new ArrayList like down:
ArrayList<String> otherList = new ArrayList<>();
for(String s : first) {
if(!otherList.contains(s))
otherList.add(s);
}
A lot of post in internet are all speaking to assign my Arraylist to a List , Set , HashTable or TreeSet. Can anyone explain the difference in theory and whitch one is the best tu use in practice ? thnks for your time guys.