A lot of people are saying that once you get to the size where speed is actually a concern that HashSet<T> will always beat List<T>, but that depends on what you are doing. Let’s say you have a List<T> that will only ever have on average 5 items in it. Over a large number of … Read more
Streams In Java 8+ you can make a stream of your int array. Call either Arrays.stream or IntStream.of. Call IntStream#boxed to use boxing conversion from int primitive to Integer objects. Collect into a list using Stream.collect( Collectors.toList() ). Or more simply in Java 16+, call Stream#toList(). Example: int[] ints = {1,2,3}; List<Integer> list = Arrays.stream(ints).boxed().collect(Collectors.toList()); … Read more
If you’re using .NET 3.5, you can use HashSet<T>. It’s true that .NET doesn’t cater for sets as well as Java does though. The Wintellect PowerCollections may help too.
If you don’t want duplicates in a Collection, you should consider why you’re using a Collection that allows duplicates. The easiest way to remove repeated elements is to add the contents to a Set (which will not allow duplicates) and then add the Set back to the ArrayList: Set<String> set = new HashSet<>(yourList); yourList.clear(); yourList.addAll(set); … Read more
Use: if my_item in some_list: … Also, inverse operation: if my_item not in some_list: … It works fine for lists, tuples, sets and dicts (check keys). Note that this is an O(n) operation in lists and tuples, but an O(1) operation in sets and dicts.
List iterators guarantee first and foremost that you get the list’s elements in the internal order of the list (aka. insertion order). More specifically it is in the order you’ve inserted the elements or on how you’ve manipulated the list. Sorting can be seen as a manipulation of the data structure, and there are several … Read more
Consider distinct to be a stateful filter. Here is a function that returns a predicate that maintains state about what it’s seen previously, and that returns whether the given element was seen for the first time: public static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) { Set<Object> seen = ConcurrentHashMap.newKeySet(); return t -> seen.add(keyExtractor.apply(t)); } … Read more
Convert comma separated String to List List<String> items = Arrays.asList(str.split(“\\s*,\\s*”)); The above code splits the string on a delimiter defined as: zero or more whitespace, a literal comma, zero or more whitespace which will place the words into the list and collapse any whitespace between the words and commas. Please note that this returns simply … Read more
There’s no built in type for ConcurrentHashSet because you can always derive a set from a map. Since there are many types of maps, you use a method to produce a set from a given map (or map class). Prior to Java 8, you produce a concurrent hash set backed by a concurrent hash map, … Read more
Same way as you would in JavaScript. delete myArray[key]; Note that this sets the element to undefined. Better to use the Array.prototype.splice function: const index = myArray.indexOf(key, 0); if (index > -1) { myArray.splice(index, 1); }