JS Data Structure Notes

What is a Data Structure?

Data structures are collections of values, the relationships among them, and the functions or operations that can be applied to the data.

1. Hash Table (a.k.a. Hash Map)

  • used to store key-value pairs
  • keys in a hash-table are not ordered
  • very fast CRUD functionality.
  • great for non-sequential data

Javascript's Object and Map are both hashes.

Color Example

const colors = ['#ff343', '#ff939', '#ff920'];
// before hashing
colors[2];
// after hashing
colors['cyan'];

The 'colors' listed are not very 'human readable'. Hash table to the rescue!

Basic gist of a hash function is such that every time a unique input gets passed in, only one unique output is returned.

pink => 1
1 => pink

to implement a rudimentary hash function we can use the charCodeAt() function

"a".charCodeAt(0) // 97, 97 is the char code at the 0th (first) value of the string on which the charCodeAt() function was called.
"hi".charCodeAt(0) // 104
"hi".charCodeAt(1) // 105
// NEAT TRICK if you subtract 96, this gives us the 'alphabetic ranking', aka, "a" is the 1st letter in the alphabet.
"a".charCodeAt(0) - 96 // 1

We can leverage the modulo operator to constrain the hash output beneath a chosen value.

52 % 11 // 8
2351431234 % 11 // 9

whatever number we modulo by, we are guaranteed to get an output that is smaller than that number, no matter how large the first number is.

What is a Graph?

A graph is a collection of nodes and connections between those nodes.

  • there are no entry points, or start/finish. The nodes are treated equally, and the connections between them are part of the definition of the graph
  • great fro recommendations and overlap analysis.
  • i.e. two video games are linked by "war", "space", and "future", nodes.
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