Looping through each combination of elements in a Map

Question

Looping through each combination of elements in a Map

I have a Map containing Shape objects with unique IDs assigned as keys. My goal is to loop through every pair of Shapes in the Map, ensuring that each pair is only processed once.

While I am aware of options like forEach or for..of for looping, I'm struggling to figure out how to avoid duplicate pairs efficiently.

shapes.forEach((shape1, shapeId1) => {
    shapes.forEach((shape2, shapeId2) => {
        // processing each pair multiple times
    });
});

javascript arrays typescript object

Answer 1

Answer №1

To start, my recommendation would be to convert the Map into an array of its entries:

const entryArray = Array.from(shapes.entries());

After that, you have the choice to iterate through pairs using either a traditional for loop:

console.log("FOR LOOP");
for (let i = 0; i < entryArray.length; i++) {
  const [shapeId1, shape1] = entryArray[i];
  for (let j = i + 1; j < entryArray.length; j++) {
    const [shapeId2, shape2] = entryArray[j];
    console.log(shapeId1, shapeId2);
  }
}

Alternatively, you can use the functional forEach array methods:

console.log("FOREACH");
entryArray.forEach(([shapeId1, shape1], i) =>
  entryArray.slice(i + 1).forEach(([shapeId2, shape2]) => {
    console.log(shapeId1, shapeId2);
  })
);

In both cases, duplicates are avoided by ensuring the inner loop only iterates over elements that come after the index of the outer loop. Regarding your types for Shape and id, assuming this structure:

interface Shape {
  area: number;
}

const shapes: Map<string, Shape> = new Map([
  ["a", { area: 1 }],
  ["b", { area: 2 }],
  ["c", { area: 3 }]
]);

The provided code will produce the following results:

FOR LOOP
a b
a c
b c
FOREACH
a b
a c
b c

As showcased, unique pairs are obtained. I hope this explanation aids you in your endeavors! Best of luck.

Link to code

Answer 2

To start, my recommendation would be to convert the Map into an array of its entries:

const entryArray = Array.from(shapes.entries());

After that, you have the choice to iterate through pairs using either a traditional for loop:

console.log("FOR LOOP");
for (let i = 0; i < entryArray.length; i++) {
  const [shapeId1, shape1] = entryArray[i];
  for (let j = i + 1; j < entryArray.length; j++) {
    const [shapeId2, shape2] = entryArray[j];
    console.log(shapeId1, shapeId2);
  }
}

Alternatively, you can use the functional forEach array methods:

console.log("FOREACH");
entryArray.forEach(([shapeId1, shape1], i) =>
  entryArray.slice(i + 1).forEach(([shapeId2, shape2]) => {
    console.log(shapeId1, shapeId2);
  })
);

In both cases, duplicates are avoided by ensuring the inner loop only iterates over elements that come after the index of the outer loop. Regarding your types for Shape and id, assuming this structure:

interface Shape {
  area: number;
}

const shapes: Map<string, Shape> = new Map([
  ["a", { area: 1 }],
  ["b", { area: 2 }],
  ["c", { area: 3 }]
]);

The provided code will produce the following results:

FOR LOOP
a b
a c
b c
FOREACH
a b
a c
b c

As showcased, unique pairs are obtained. I hope this explanation aids you in your endeavors! Best of luck.

Link to code

Answer 3

Answer №2

To avoid processing two pairs, you can utilize two for loops with an index and initiate the nested iteration from the main index + 1.

const numbers = [1,2,3,4];


for (let x = 0; x<numbers.length-1; x++) {
  for (let y = x+1; y<numbers.length; y++) {
    console.log(`${numbers[x]} - ${numbers[y]}`)
  }
}

Answer 4

To avoid processing two pairs, you can utilize two for loops with an index and initiate the nested iteration from the main index + 1.

const numbers = [1,2,3,4];


for (let x = 0; x<numbers.length-1; x++) {
  for (let y = x+1; y<numbers.length; y++) {
    console.log(`${numbers[x]} - ${numbers[y]}`)
  }
}

Answer 5

Answer №3

To find unique pairs in a collection of shapes, utilize a Set with the two indexes:

let pairIndexes = new Set();

shapes.forEach((shape1, shapeIndex1) => {

    shapes.forEach((shape2, shapeIndex2) => {

        if (pairIndexes.has(`${shapeIndex1}-${shapeIndex2}`) || pairIndexes.has(`${shapeIndex2}-${shapeIndex1}`)) return;
        pairIndexes.add(`${shapeIndex1}-${shapeIndex2}`);

    });

});

Answer 6

To find unique pairs in a collection of shapes, utilize a Set with the two indexes:

let pairIndexes = new Set();

shapes.forEach((shape1, shapeIndex1) => {

    shapes.forEach((shape2, shapeIndex2) => {

        if (pairIndexes.has(`${shapeIndex1}-${shapeIndex2}`) || pairIndexes.has(`${shapeIndex2}-${shapeIndex1}`)) return;
        pairIndexes.add(`${shapeIndex1}-${shapeIndex2}`);

    });

});

Looping through each combination of elements in a Map

Answer №1

Answer №2

Answer №3

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