sequence-n-x v0.0.0

Sequence-N-X

Overview

Module used for generating sequences of indefinite length using a function with ability to reference previous elements It produces values when needed and stores them after they were required for the first time

Installation

$ npm i --save sequence-n-x

Examples

Fibonacci numbers

const sq = require("sequence-n-x");
const fibonacciNumbers = sq ( (index,n)=> n(-1) + n(-2),[1,1])
console.log(fibonacciNumbers.take (10)); // 1 1 2 3 5 8 13 21 34 55

Triangular numbers using formula based on index

const triangularNumbers1 = sq((i,n) => (i * (i + 1)) / 2);
console.log(triangularNumbers1.take (5); // 0 1 3 6 10

Triangular numbers with calculating next element based on previous

const triangularNumbers1 = sq((i,n) => n(-1) + i);
console.log(triangularNumbers1.take (5); // 0 1 3 6 10

Range of integers starting with 0

console.log(sq().take(5)); // 0 1 2 3 4

Interface

Creating an object

const mySequence = sq(generatorFunction, initialValues, generateAtCreation);

Generator function

A function that create and return element of a sequence

const generatorFunctionTriangular = (index , n) => n(-1)+i;
const  generatorFunctionFibo = (i,n)=> n(-1)+n(-2);

where index is a position in a sequence starting with 0 (similar to iterating over arrays with ar.map((x,i)=>... ) n is a function that as an argument takes index of another element relative to one that is being created and returns it's value n(-1) is previous element, n(-2) is element before that n should be negative integer if -n > index then ( attempt to get element with index < 0) 0th element will be used

Note: instead of numbers other types (strings objects arrays etc) can be used as a return value If omitted (i)=>i would be used as default, producing 0 1 2 3... sequence

###Initial values Array of values that start a sequence and should be defined by hand. 1,1 in Fibonacci numbers If there is a single value, it can be passed as a single value, not like an array

Default: 0

generateAtCreation

Normally new elements would be produced only when they are required, but user can specify number of elements that would be produced at the beginning Default: 0

Retrieving values

mySequence.take(amount)

returns array containing elements from 0th to amounth

mySequence.slice(start,end)

returns array containing elements from start to end (zero based indexes)

mySequence.get(index)

returns one element of provided index

Value generation details

By default elements are generated when retrieving methods (take slice get) are called Each element gets generated only once and then stored

    s1.take (5)
    s1.take (10) // returns 0 to 10 but produces only elements 6 to 10

When elements starting from specific index are needed whole range up to the last one is generated

    s2.slice(7,10) // returns 7 to 10 but produces 0 to 10
    s2.get ( 20) // produces 0 to 20