Let say I have an array of points = [[1,3],[-2,2] which represent x, y coordinates.
I want to access these values (distances of two points) at the points [x,y]. I just can’t get my mind wrapped on how these two approaches are different.
Why do I have access to one hash maps value, and the next I received undefined?
function getDistances1(points) {
const lookup = new Map();
// Destructing with a for of
for (const [x, y] of points) {
let distance = Math.sqrt((x**2) + (y**2))
lookup.set([x,y], distance)
}
// I won't have access to the value of the array when I try to retrieve the value from the hash map
return lookup;
}
function getDistances2(points) {
const lookup = new Map();
// Destructing with a traditional for loop
for (let i = 0; i < points.length; i++) {
// Destruct this way
const [x, y] = [...points[i]]
let distance = Math.sqrt((x**2) + (y**2))
lookup.set(points[i], distance)
}
// I have access to this points value
return lookup; //
}
const coordinates = [[1,3],[-2,2]]
const distance1 = getDistances1(coordinates);
const distance2 = getDistances2(coordinates);
console.log(distance2.get(coordinates[0])) //-> 3.1622776601683795 ;
console.log(distance1.get(coordinates[0])) // undefinedAnswer
The reason that getDistances1 doesn’t work is that you’re creating separate x and y variables here:
for (const [x, y] of points) {
and then creating a new array here:
lookup.set([x,y], distance)
But you’re trying to look up the information using the array that was in points. The information isn’t stored under that array, you’ve stored it under a new array instead.
You could do this (see *** comments):
function getDistances1(points) {
const lookup = new Map();
// Destructing with a for of
for (const point of points) { // *** Use the array from `points
const [x, y] = point; // *** Convenient destructuring
let distance = Math.sqrt((x**2) + (y**2))
lookup.set(point, distance); // *** Store keyed by the array
}
return lookup;
}