Another option, if portability is not your main concern, is to use associative arrays that are built in to the shell. This should work in bash 4.0 (available now on most major distros, though not on OS X unless you install it yourself), ksh, and zsh: declare -A newmap newmap[name]=”Irfan Zulfiqar” newmap[designation]=SSE newmap[company]=”My Own Company” … Read more
I’ve had nice results with djb2 by Dan Bernstein. unsigned long hash(unsigned char *str) { unsigned long hash = 5381; int c; while (c = *str++) hash = ((hash << 5) + hash) + c; /* hash * 33 + c */ return hash; }
Advantages of tries: The basics: Predictable O(k) lookup time where k is the size of the key Lookup can take less than k time if it’s not there Supports ordered traversal No need for a hash function Deletion is straightforward New operations: You can quickly look up prefixes of keys, enumerate all entries with a … Read more
Usually hashes wouldn’t do sums, otherwise stop and pots will have the same hash. and you wouldn’t limit it to the first n characters because otherwise house and houses would have the same hash. Generally hashs take values and multiply it by a prime number (makes it more likely to generate unique hashes) So you … Read more
An easy, correct way to implement __hash__() is to use a key tuple. It won’t be as fast as a specialized hash, but if you need that then you should probably implement the type in C. Here’s an example of using a key for hash and equality: class A: def __key(self): return (self.attr_a, self.attr_b, self.attr_c) … Read more
Yes, it is a hash mapping or hash table. You can read a description of python’s dict implementation, as written by Tim Peters, here. That’s why you can’t use something ‘not hashable’ as a dict key, like a list: >>> a = {} >>> b = [‘some’, ‘list’] >>> hash(b) Traceback (most recent call last): … Read more
System.Collections.Generic.Dictionary<TKey, TValue> and System.Collections.Hashtable classes both maintain a hash table data structure internally. None of them guarantee preserving the order of items. Leaving boxing/unboxing issues aside, most of the time, they should have very similar performance. The primary structural difference between them is that Dictionary relies on chaining (maintaining a list of items for each … Read more
By definition, the put command replaces the previous value associated with the given key in the map (conceptually like an array indexing operation for primitive types). The map simply drops its reference to the value. If nothing else holds a reference to the object, that object becomes eligible for garbage collection. Additionally, Java returns any … Read more
Here’s an explanation in layman’s terms. Let’s assume you want to fill up a library with books and not just stuff them in there, but you want to be able to easily find them again when you need them. So, you decide that if the person that wants to read a book knows the title … Read more
Use JavaScript objects as associative arrays. Associative Array: In simple words associative arrays use Strings instead of Integer numbers as index. Create an object with var dictionary = {}; JavaScript allows you to add properties to objects by using the following syntax: Object.yourProperty = value; An alternate syntax for the same is: Object[“yourProperty”] = value; … Read more