Is checking for key existence in HashMap always necessary? I have a HashMap with say a 1000 entries and I am looking at improving the efficiency. If the HashMap is being accessed very frequently, then checking for the key existence at every access will lead to a large overhead. Instead if the key is not … Read more
How to convert a ruby hash object to JSON? So I am trying this example below & it doesn’t work? I was looking at the RubyDoc and obviously Hash object doesn’t have a to_json method. But I am reading on blogs that Rails supports active_record.to_json and also supports hash#to_json. I can understand ActiveRecord is a … Read more
Coming from a Java world into a C# one is there a HashMap equivalent? If not what would you recommend? 7 Answers 7
What is the difference between the following maps I create (in another question, people answered using them seemingly interchangeably and I’m wondering if/how they are different): HashMap<String, Object> map = new HashMap<String, Object>(); Map<String, Object> map = new HashMap<String, Object>(); 13 Answers 13
As made clear in update 3 on this answer, this notation: var hash = {}; hash[X] does not actually hash the object X; it actually just converts X to a string (via .toString() if it’s an object, or some other built-in conversions for various primitive types) and then looks that string up, without hashing it, … Read more
I have a Map that has strings for both keys and values. Data is like following: “question1”, “1” “question9”, “1” “question2”, “4” “question5”, “2” I want to sort the map based on its keys. So, in the end, I will have question1, question2, question3….and so on. Eventually, I am trying to get two strings out … Read more
Use Case The use case is to convert an array of objects into a hash map based on string or function provided to evaluate and use as the key in the hash map and value as an object itself. A common case of using this is converting an array of objects into a hash map … Read more
If I have the value “foo”, and a HashMap<String> ftw for which ftw.containsValue(“foo”) returns true, how can I get the corresponding key? Do I have to loop through the hashmap? What is the best way to do that? 39 s 39
To add a new pair to Hash I do: {:a => 1, :b => 2}.merge!({:c => 3}) #=> {:a => 1, :b => 2, :c => 3} Is there a similar way to delete a key from Hash ? This works: {:a => 1, :b => 2}.reject! { |k| k == :a } #=> {:b … Read more
HashSet is based on HashMap. If we look at HashSet<E> implementation, everything is been managed under HashMap<E,Object>. <E> is used as a key of HashMap. And we know that HashMap is not thread safe. That is why we have ConcurrentHashMap in Java. Based on this, I am confused that why we don’t have a ConcurrentHashSet … Read more
