nvector.ts

// Objects with only numeric properties that can be treated as a n-dimensional vector

export type Vector<T> = {
  [P in keyof T]: number
};

const vextend = <T>(obj: Vector<T>, key: string, val: number): Vector<T> => Object.assign(obj, { [key]: val });


export const vreduce = <T, R>(obj: Vector<T>, reducer: (agg: R, [key, val]: [string, number]) => R, init: R): R =>
  Object.entries(obj)
    .reduce((agg, [key, val]: [string, number]) => reducer(agg, [key, val]), init);


export const vmap = <T>(v: Vector<T>, mapper: (key: keyof T, val: number) => number): Vector<T> =>
  vreduce(v, (agg, [key, val]) => vextend(v, key, mapper(key as keyof T, val)),
    {}
  ) as Vector<T>; // cannot make ts induce that mapping over all keys will transform a {} into the full Vector<T>


export const vmult = <T>(v: Vector<T>, k: number): Vector<T> =>
  vmap(v, (key, val) => val * k);


export const vplus = <T>(v1: Vector<T>, v2: Vector<T>): Vector<T> =>
  vmap(v1, (key, val) => val + v2[key]);


export const vlength = <T>(v: Vector<T>): number =>
  vreduce(v, (agg, [key, val]) => agg + val * val, 0);