What is the difference between Collection and List in Java?
What is the difference between Collection and List in Java? When should I use which? 7 Answers 7
collections
Select N random elements from a List in C#
I need a quick algorithm to select 5 random elements from a generic list. For example, I’d like to get 5 random elements from a List<string>. 32 Answers 32 Using linq: YourList.OrderBy(x => rnd.Next()).Take(5)
Is there a built-in method to compare collections?
I would like to compare the contents of a couple of collections in my Equals method. I have a Dictionary and an IList. Is there a built-in method to do this? Edited: I want to compare two Dictionaries and two ILists, so I think what equality means is clear – if the two dictionaries contain … Read more
Difference between HashSet and HashMap?
Apart from the fact that HashSet does not allow duplicate values, what is the difference between HashMap and HashSet? I mean implementation wise? It’s a little bit vague because both use hash tables to store values. 20 Answers 20
Assert equals between 2 Lists in Junit
How can I make an equality assertion between lists in a JUnit test case? Equality should be between the content of the list. For example: List<String> numbers = Arrays.asList(“one”, “two”, “three”); List<String> numbers2 = Arrays.asList(“one”, “two”, “three”); List<String> numbers3 = Arrays.asList(“one”, “two”, “four”); // numbers should be equal to numbers2 //numbers should not be equal … Read more
count vs length vs size in a collection
From using a number of programming languages and libraries I have noticed various terms used for the total number of elements in a collection. The most common seem to be length, count, and size. eg. array.length vector.size() collection.count Is there any preferred term to be used? Does it depend on what type of collection it … Read more
How can I initialize an ArrayList with all zeroes in Java?
It looks like arraylist is not doing its job for presizing: // presizing ArrayList<Integer> list = new ArrayList<Integer>(60); Afterwards when I try to access it: list.get(5) Instead of returning 0 it throws IndexOutOfBoundsException: Index 5 out of bounds for length 0. Is there a way to initialize all elements to 0 of an exact size … Read more
Case-INsensitive Dictionary with string key-type in C#
If I have a Dictionary<String,…> is it possible to make methods like ContainsKey case-insensitive? This seemed related, but I didn’t understand it properly: c# Dictionary: making the Key case-insensitive through declarations 6 Answers 6
Immutable vs Unmodifiable collection [duplicate]
This question already has answers here: Java Immutable Collections (7 answers) Closed 2 days ago. From the Collections Framework Overview: Collections that do not support modification operations (such as add, remove and clear) are referred to as unmodifiable. Collections that are not unmodifiable are modifiable. Collections that additionally guarantee that no change in the Collection … Read more
How to sort Counter by value? – python
Other than doing list comprehensions of reversed list comprehension, is there a pythonic way to sort Counter by value? If so, it is faster than this: >>> from collections import Counter >>> x = Counter({‘a’:5, ‘b’:3, ‘c’:7}) >>> sorted(x) [‘a’, ‘b’, ‘c’] >>> sorted(x.items()) [(‘a’, 5), (‘b’, 3), (‘c’, 7)] >>> [(l,k) for k,l in … Read more
