arrays

Complete

lang
/
js

Summary

Concept of a buffer

// initialisation
const x = [1, 2, 3];
// indexing
const a = x[1];
// assignment
x[4] = 4;
// length
array_length(x); // 5

Concept

An array is a sequence of elements
Elements in the array can be initialised, assigned or indexed

Random access -> constant time read and write, except if writing to an index larger than array length

Application

Array processing functions
Main idea:

iterate through the elements in the array

function map_array(f, arr) {
	const len = array_length(arr);     
	function iter(i) {         
		if (i < len) {             
			arr[i] = f(arr[i]);             
			iter(i + 1);
		}    
	}     
	iter(0); 
}
const seq = [3, 1, 5]; 
map_array(x => 2 * x, seq); 
seq; // -> [6, 2, 10];  destructive operation 

function array_1_to_n(n) {     
	const a = [];     
	function iter(i) {         
		if (i < n) {             
			a[i] = i + 1;             
			iter(i + 1);         
		}     
	}     
	iter(0);     
	return a; 
} 
array_1_to_n(3);  // -> [1, 2, 3]

Matricies as 2d arrays, 3 by 4 matrix

const matrix = [[1,  2,  3,  4],
				[5,  6,  7,  8],
				[9, 10, 11, 12]]

Note

Some programming languages, ie. Python, do not allow assignment to indexes out of the range of the array
In Source/JS, the value is assigned regardless if the index is already initialised, any in-between indices are left as undefined