将3层阵列映射到对象集合

Question

I'm struggling to get a 3 tier grouping of arrays to map correctly to a single collection of objects with each tier as a key name of the object and the array value as the key value.

The three arrays relate to each other by tier and are structured as follows:

{
  tier1: ['tier1-item1', 'tier1-item2'],
  tier2: ['tier2-item1', 'tier2-item2', 'tier2-item3', 'tier2-item4', 'tier2-item5'],
  tier3: ['tier3-item1', 'tier3-item2', 'tier3-item3']
}

They need to result in an array of objects in as follows:

[
  {tier1: "tier1-item1", tier2: "tier2-item1", tier3: "tier3-item1"},
  {tier1: "tier1-item1", tier2: "tier2-item2", tier3: "tier3-item1"},
  {tier1: "tier1-item1", tier2: "tier2-item3", tier3: "tier3-item1"},
  {tier1: "tier1-item1", tier2: "tier2-item4", tier3: "tier3-item1"},
  {tier1: "tier1-item1", tier2: "tier2-item5", tier3: "tier3-item1"},

  {tier1: "tier1-item2", tier2: "tier2-item1", tier3: "tier3-item1"},
  {tier1: "tier1-item2", tier2: "tier2-item2", tier3: "tier3-item1"},
  {tier1: "tier1-item2", tier2: "tier2-item3", tier3: "tier3-item1"},
  {tier1: "tier1-item2", tier2: "tier2-item4", tier3: "tier3-item1"},
  {tier1: "tier1-item2", tier2: "tier2-item5", tier3: "tier3-item1"},

  {tier1: "tier1-item1", tier2: "tier2-item1", tier3: "tier3-item2"},
  {tier1: "tier1-item1", tier2: "tier2-item2", tier3: "tier3-item2"},
  {tier1: "tier1-item1", tier2: "tier2-item3", tier3: "tier3-item2"},
  {tier1: "tier1-item1", tier2: "tier2-item4", tier3: "tier3-item2"},
  {tier1: "tier1-item1", tier2: "tier2-item5", tier3: "tier3-item2"},

  {tier1: "tier1-item2", tier2: "tier2-item1", tier3: "tier3-item2"},
  {tier1: "tier1-item2", tier2: "tier2-item2", tier3: "tier3-item2"},
  {tier1: "tier1-item2", tier2: "tier2-item3", tier3: "tier3-item2"},
  {tier1: "tier1-item2", tier2: "tier2-item4", tier3: "tier3-item2"},
  {tier1: "tier1-item2", tier2: "tier2-item5", tier3: "tier3-item2"},

  {tier1: "tier1-item1", tier2: "tier2-item1", tier3: "tier3-item3"},
  {tier1: "tier1-item1", tier2: "tier2-item2", tier3: "tier3-item3"},
  {tier1: "tier1-item1", tier2: "tier2-item3", tier3: "tier3-item3"},
  {tier1: "tier1-item1", tier2: "tier2-item4", tier3: "tier3-item3"},
  {tier1: "tier1-item1", tier2: "tier2-item5", tier3: "tier3-item3"},

  {tier1: "tier1-item2", tier2: "tier2-item1", tier3: "tier3-item3"},
  {tier1: "tier1-item2", tier2: "tier2-item2", tier3: "tier3-item3"},
  {tier1: "tier1-item2", tier2: "tier2-item3", tier3: "tier3-item3"},
  {tier1: "tier1-item2", tier2: "tier2-item4", tier3: "tier3-item3"},
  {tier1: "tier1-item2", tier2: "tier2-item5", tier3: "tier3-item3"},
]

so there is an object for all possible combinations of items.

I'm not necessarily looking for code examples, although they're welcome, more of a conceptual push in the right direction, es5+.

Answer 1

You require a simple nested loop as follows:

function(input) {
  let arr = [];
  for (let i = 0; i < input["tier1"].length; i++) {
    for (let j = 0; j < input["tier2"].length; j++) {
      for (let k = 0; k < input["tier3"].length; k++) {
        let obj = {
          tier1: input["tier1"][i],
          tier2: input["tier2"][j],
          tier3: input["tier3"][k]
        };
        arr.push(obj);
      }
    }
  }
  return arr;
}

For a generic solution for n-such tiers, we could do it without nesting as follows:

function allCombinations(input) {
  let result = [];
  (function recurse(input, n, outObject, outputArray) {
    if (n > Object.keys(input).length) { 
      outputArray.push(outObject);
      return;
    }
    let str = "tier" + n;
    for (let i = 0; i < input[str].length; i++) {
      let obj = Object.assign({}, outObject);
      obj[str] = input[str][i];
      recurse(input, n+1, obj, outputArray);
    }
  })(input, 1, {}, result);
  return result;
}

Basically, we choose every element of a tier, clone it and recurse it for the next tier till we reach the end.

Answer 2

You can use reduce to iterate all the data and Set to create an array with unique values.

// pass to reduce an empty object as initial value, let's call it accumulator
data.reduce((accumulator, currentValue, index) => {
  // get single object and iterate its keys
  for(let key in currentValue) {
    // check if accumulator contains already the key
    // if yes
    if (accumulator.hasOwnProperty(key)) {
      // update the Set (internally with automaticcaly remove the duplicate values)
      accumulator[key].add(currentValue[key])
    } else {
      // if not, create the Set
      accumulator[key] = new Set([currentValue[key]]);
    }
  }
  // Have we finish looping?
  // If yes, we have to convert Set to Array
  if (index === data.length - 1) {
    const finalObject = {};
    Object.keys(accumulator).forEach(singleKey => {
      finalObject[singleKey] = Array.from(accumulator[singleKey]);
    })
    return finalObject;
  } else {
    // if not we continue
   return accumulator 
  }
}, {});