Arraylist Filter [Duplicate]

Question

How can you filter out something from a Java ArrayList like if you have:

How are you
How you doing
Joe
Mike

And the filter is "How" it will remove Joe and Mike.

Accepted Answer

In java-8, they introduced the method removeIf which takes a Predicate as parameter.

So it will be easy as:

List<String> list = new ArrayList<>(Arrays.asList("How are you",
                                                  "How you doing",
                                                  "Joe",
                                                  "Mike"));
list.removeIf(s -> !s.contains("How"));

Accepted Answer

Probably the best way is to use Guava

List<String> list = new ArrayList<String>();
list.add("How are you");
list.add("How you doing");
list.add("Joe");
list.add("Mike");
    
Collection<String> filtered = Collections2.filter(list,
    Predicates.containsPattern("How"));
print(filtered);

prints

How are you
How you doing

In case you want to get the filtered collection as a list, you can use this (also from Guava):

List<String> filteredList = Lists.newArrayList(Collections2.filter(
    list, Predicates.containsPattern("How")));

Answer 3

Iterate through the list and check if contains your string "How" and if it does then remove. You can use following code:

// need to construct a new ArrayList otherwise remove operation will not be supported
List<String> list = new ArrayList<String>(Arrays.asList(new String[] 
                                  {"How are you?", "How you doing?","Joe", "Mike"}));
System.out.println("List Before: " + list);
for (Iterator<String> it=list.iterator(); it.hasNext();) {
    if (!it.next().contains("How"))
        it.remove(); // NOTE: Iterator's remove method, not ArrayList's, is used.
}
System.out.println("List After: " + list);

OUTPUT:

List Before: [How are you?, How you doing?, Joe, Mike]
List After: [How are you?, How you doing?]

Answer 4

write your self a filter function

 public<T> List<T> filter(Predicate<T> criteria, List<T> list) {
        return list.stream().filter(criteria).collect(Collectors.<T>toList());
 }

And then use

    list = new Test().filter(x -> x > 2, list);

This is the most neat version in Java, but needs JDK 1.8 to support lambda calculus

Answer 5

I agree with a previous answer that Google Guava is probably helping a lot here, readability-wise:

final Iterables.removeIf(list, new Predicate<String>() {
    @Override
    public boolean apply(String input) {
        if(input.contains("How")) { //or more complex pattern matching
            return true;
        }
        return false;
    }
});

Please note that this is basically a duplicate of Guava - How to remove from a list, based on a predicate, keeping track of what was removed?

Answer 6

As you didn't give us very much information, I'm assuming the language you're writing the code in is C#. First of all: Prefer System.Collections.Generic.List over an ArrayList. Secondly: One way would be to loop through every item in the list and check whether it contains "How". Another way would be to use LINQ. Here's a quick example that filters out every item which doesn't contain "How":

var list = new List<string>();
list.AddRange(new string[] {
    "How are you?",
    "How you doing?",
    "Joe",
    "Mike", });

foreach (string str in list.Where(s => s.Contains("How")))
{
    Console.WriteLine(str);
}
Console.ReadLine();

Arraylist Filter [Duplicate]

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6 Answers

Robert Thorne