mortensen mortensen - 2 months ago 6
Javascript Question

Generating all possible true/false combinations

I want to create an array of all possible combinations of three variables that can either be true or false (i.e. 8 possible combinations).

I am trying to create the cube in the top left corner at this image

enter image description here

So the output should be something like

points = [
// first square
{
id: '000',
truths: [false, false, false]
position: [0, 0]
},
{
id: '100',
truths: [true, false, false]
position: [5, 0]
},
{
id: '010',
truths: [false, true, false]
position: [0, 5]
},
{
id: '110',
truths: [true, true, false]
position: [5, 5]
},
// second square
{
id: '001',
truths: [false, false, true]
position: [2.5, 2.5]
},
{
id: '101',
truths: [true, false, true]
position: [7.5, 2.5]
},
{
id: '011',
truths: [false, true, true]
position: [2.5, 7.5]
},
{
id: '111',
truths: [true, true, true]
position: [7.5, 7.5]
},
];

lines = [
{ from: '000', to: '100' },
{ from: '000', to: '010' },
{ from: '000', to: '001' },

{ from: '100', to: '101' },
{ from: '100', to: '110' },

{ from: '001', to: '101' },
{ from: '001', to: '011' },

{ from: '101', to: '001' },
{ from: '101', to: '111' },

...
]


I don't know how to go through all possible truth values and create these points.

One approach could be to use a for loop

for (var i=0; i<Math.pow(2, 3); i++) {
...
}


but it doesn't help me assigning the possible truth values.

Answer

Everything in a computer is already binary. You don't need any fancy Math.pow or similar.

for (let i = 0; i < 1 << 3; i++) {
  console.log([!!(i & (1<<2)), !!(i & (1<<1)), !!(i & 1)]);
}

While this looks nice and short, i am actually not a fan of !! or magic numbers. I always fall for these tricks when writing snippets though. Therefore will attempt to give a slightly cleaner version:

const AMOUNT_OF_VARIABLES = 3;

for (let i = 0; i < (1 << AMOUNT_OF_VARIABLES); i++) {
  let boolArr = [];
  
  //Increasing or decreasing depending on which direction
  //you want your array to represent the binary number
  for (let j = AMOUNT_OF_VARIABLES - 1; j >= 0; j--) {
    boolArr.push(Boolean(i & (1 << j)));
  }
  
  console.log(boolArr);
}