let input = [
  [[1, 4], [40, 4]],
  [[1, 5], [40, 5]],
  [[4, 7], [4, 24]],
  [[1, 9], [4, 1]],
  [[1, 2], [6, 4]],
  [[80, 4], [90, 4]],
  [[4, 1], [4, 40]],
  [[4, 35], [4, 29]],
  [[4, 28], [4, 35]],
  [[5, 3.6], [9, 5.2]],
]; // Input

Output = [
  [[[1, 4], [40, 4]], [[80, 4], [90, 4]]],
  [[[1, 5], [40, 5]]],
  [[[4, 7], [4, 24]], [[4, 1], [4, 40]]],
  [[[4, 35], [4, 29]], [[4, 28], [4, 35]]],
  [[[1, 9], [4, 1]]],
  [[[1, 2], [6, 4]], [[5, 3.6], [9, 5.2]]],
];

If given an input of series of each start and end coordinates of a line, for example, [[1,4],[40,4]] means that it has 2 points connecting [1,4] and [40,4] to form a straight line. My objective now is to group all those lines which share the same equation y=mx+c, together into a nested array as shown above. For example,

[[1,4],[40,4]] and [[80,4],[90,4]] share the same linear equation y=4

[[4,7],[4,24]],[[4,1],[4,40]]      share the same linear equation x=4

 [[1,2],[6,4]] and [[5,3.6],[9,5.2]]  share the same linear equation y=0.4x+1.6

[[1,9],[4,1]]   is alone and it has the linear equation of -2.67x+11.67

Here is my working codepen demo

I know how to code out to find those m and c in y=mx+c, but the problem is when for example,[[4,7],[4,24]] and [[4,1],[4,40]] , the m gradient becomes infinity which unsolvable.

Can anyone please guide me on this on how to get the correct output?

>Solution :

You can calculate the slope equation for each set of points and assign it to each array item, then group:

const input=[[[1,4],[40,4]],[[1,5],[40,5]],[[4,7],[4,24]],[[1,9],[4,1]],[[1,2],[6,4]],[[80,4],[90,4]],[[4,1],[4,40]],[[4,35],[4,29]],[[4,28],[4,35]],[[5,3.6],[9,5.2]]];

const inputsWithSlope = input.map((points) => {
  const [[x, y], [x1, y1]] = points;
  const slope = (y1 - y) / (x1 - x)
  const b = y1 - slope * x1
  return {
    points,
    line: x1 == x ? `x = ${x}` : `y = ${slope}x + ${b}`
  }
})

const res = inputsWithSlope.reduce((acc, curr) => {
  const accProp = acc[curr.line]
  acc[curr.line] = !accProp ? [curr.points] : [...accProp, curr.points]
  return acc
}, {})
const result = Object.values(res)
console.log(JSON.stringify(result))