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Questions tagged [hashtable]

A hash table in programming is a collection that uses a hash function to map identifying values (keys) to their associated values.

The basic advantage of a hash table is that they provide very efficient lookup and search functionality. Unlike many other linear collection types (such as arrays and linked lists), one does not have to loop through all the elements in a hash table searching for a particular entity.

For Java: https://docs.oracle.com/javase/8/docs/api/java/util/Hashtable.html

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Hash table - why is it faster than arrays?

In cases where I have a key for each element and I don't know the index of the element into an array, hashtables perform better than arrays (O(1) vs O(n)). Why is that? I mean: I have a key, I hash it.. I have the hash.. shouldn't the algorithm…
Johnny Pauling
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How do I encode a JavaScript object as JSON?

Is there a good way to encode a JavaScript object as JSON? I have a list of key value pairs...where the name is from a checkbox, and the value is either true or false based on whether the box is checked or not: var values = {}; $('#checks…
daniel langer
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Looking for a good hash table implementation in C

I am primarily interested in string keys. Can someone point me towards a library?
Setjmp
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iterating through Enumeration of hastable keys throws NoSuchElementException error

I am trying to iterate through a list of keys from a hash table using enumeration however I keep getting a NoSuchElementException at the last key in list? Hashtable vars = new Hashtable(); vars.put("POSTCODE","TU1…
David Cunningham
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How do you implement GetHashCode for structure with two string, when both strings are interchangeable

I have a structure in C#: public struct UserInfo { public string str1 { get; set; } public string str2 { get; set; } } The only rule is that UserInfo(str1="AA", str2="BB").Equals(UserInfo(str1="BB",…
Graviton
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Binary Trees vs. Linked Lists vs. Hash Tables

I'm building a symbol table for a project I'm working on. I was wondering what peoples opinions are on the advantages and disadvantages of the various methods available for storing and creating a symbol table. I've done a fair bit of searching and…
benmcredmond
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Improving performance of very large dictionary in Python

I find that if I initialize an empty dictionary at the beginning, and then adding elements to the dictionary in a for loop (about 110,000 keys, the value for each key is a list, also increasing in the loop), the speed goes down as for loop goes. I…
szli
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How do I create a Dictionary that holds different types in C#

I need some sort of way to store key/value pairs where the value can be of different types. So I like to do: int i = 12; string s = "test"; double x = 24.1; Storage.Add("age", i); Storage.Add("name", s); Storage.Add("bmi", x); And later…
Enrico
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What is the true difference between a dictionary and a hash table?

I've always used dictionaries. I write in Python.
TIMEX
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Why there is a Thread.Sleep(1) in .NET internal Hashtable?

Recently I was reading implementation of .NET Hashtable and encountered piece of code that I don't understand. Part of the code is: int num3 = 0; int num4; do { num4 = this.version; bucket = bucketArray[index]; if (++num3 % 8 == 0) …
Dariusz Woźniak
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Why can't you use null as a key for a Dictionary?

Apparently, you cannot use a null for a key, even if your key is a nullable type. This code: var nullableBoolLabels = new System.Collections.Generic.Dictionary { { true, "Yes" }, { false, "No" }, { null, "(n/a)"…
devuxer
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What hashing function does Java use to implement Hashtable class?

From the book CLRS ("Introduction to Algorithms"), there are several hashing functions, such as mod, multiply, etc. What hashing function does Java use to map the keys to slots? I have seen there is a question here Hashing function used in Java…
Jackson Tale
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What is a hash map in programming and where can it be used

I have often heard people talking about hashing and hash maps and hash tables. I wanted to know what they are and where you can best use them for.
Saif Bechan
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Chained Hash Tables vs. Open-Addressed Hash Tables

Can somebody explain the main differences between (advantages / disadvantages) the two implementations? For a library, what implementation is recommended?
Andrei Ciobanu
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How does Java order items in a HashMap or a HashTable?

I was wondering how Java orders items in the Map (HashMap or Hashtable) when they are added. Are the keys ordered by the hashcode, memory reference or by allocation precedence...? It's because I've noticed same pairs in the Map are not always in the…
Eyad Salah
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