Ruby: merge nested hash
For rails 3.0.0+ or higher version there is the deep_merge function for ActiveSupport that does exactly what you ask for.
hash
Getting hash of a list of strings regardless of order
There are various different approaches here the under two main categories, each typically with their own benefits and disadvantages, in terms of effectiveness and performance. It is probably best to choose the simplest algorithm for whatever application and only use the more complex variants if necessary for whatever situation. Note that these examples use EqualityComparer<T>.Default … Read more
What hashing function does Java use to implement Hashtable class?
When a key is added to or requested from a HashMap in OpenJDK, the flow of execution is the following: The key is transformed into a 32-bit value using the developer-defined hashCode() method. The 32-bit value is then transformed by a second hash function (of which Andrew’s answer contains the source code) into an offset … Read more
How to elegantly symbolize_keys for a ‘nested’ hash
There are a few ways to do this There’s a deep_symbolize_keys method in Rails hash.deep_symbolize_keys! As mentioned by @chrisgeeq, there is a deep_transform_keys method that’s available from Rails 4. hash.deep_transform_keys(&:to_sym) There is also a bang ! version to replace the existing object. There is another method called with_indifferent_access. This allows you to access a hash … Read more
What is the true difference between a dictionary and a hash table?
A dictionary is a general concept that maps keys to values. There are many ways to implement such a mapping. A hashtable is a specific way to implement a dictionary. Besides hashtables, another common way to implement dictionaries is red-black trees. Each method has its own pros and cons. A red-black tree can always perform … Read more
Fast String Hashing Algorithm with low collision rates with 32 bit integer [closed]
Murmur Hash is pretty nice.
What’s the difference between a hash and hash reference in Perl?
A simple hash is close to an array. Their initializations even look similar. First the array: @last_name = ( “Ward”, “Cleaver”, “Fred”, “Flintstone”, “Archie”, “Bunker” ); Now let’s represent the same information with a hash (aka associative array): %last_name = ( “Ward”, “Cleaver”, “Fred”, “Flintstone”, “Archie”, “Bunker” ); Although they have the same name, the … Read more
GetHashCode() on byte[] array
Arrays in .NET don’t override Equals or GetHashCode, so the value you’ll get is basically based on reference equality (i.e. the default implementation in Object) – for value equality you’ll need to roll your own code (or find some from a third party). You may want to implement IEqualityComparer<byte[]> if you’re trying to use byte … Read more
How to call a method stored in a HashMap? (Java) [duplicate]
With Java 8+ and Lambda expressions With lambdas (available in Java 8+) we can do it as follows: class Test { public static void main(String[] args) throws Exception { Map<Character, Runnable> commands = new HashMap<>(); // Populate commands map commands.put(‘h’, () -> System.out.println(“Help”)); commands.put(‘t’, () -> System.out.println(“Teleport”)); // Invoke some command char cmd = ‘t’; … Read more
Ruby Style: How to check whether a nested hash element exists
The most obvious way to do this is to simply check each step of the way: has_children = slate[:person] && slate[:person][:children] Use of .nil? is really only required when you use false as a placeholder value, and in practice this is rare. Generally you can simply test it exists. Update: If you’re using Ruby 2.3 … Read more