How do I take an array of objects and reduce it so that data at a repeated object key is combined?

user_14830698 0
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I'm working on a react app that mimics a retail website. My main page displays an item, and below has card components of related products. When I click a button on one of the related products, I open a comparison modal that compares features of the current product and the clicked upon product. I figured that to accomplish this, I would create an array of the combined features of the clicked on product and the main page product. I've been struggling to get create an array of objects, where each unique feature has an object with data inside about the features and which product the feature belongs to.

As of right now, I've been able to get an array of all the features that the two products have, but this array has repeats if the products have overlapping features. This makes me unsure of how to render the comparison table because I was planning on mapping over the array and creating a table row for each feature. My current code to format these features is as follows:

formatFeatures: (currentProd, clickedProd) => {
let combinedFeatures = [];
if (clickedProd.features) {
  clickedProd.features.forEach(feature => {
    let obj = {}
    let vals = Object.values(feature);
    obj[vals[0]] = [vals[1], clickedProd.id]
    combinedFeatures.push(obj)
  })
}
currentProd.features.forEach(feature => {
  let obj = {}
  let vals = Object.values(feature);
  obj[vals[0]] = [vals[1], currentProd.id]
  combinedFeatures.push(obj)
})

let formattedFeatures = combinedFeatures.reduce((allFeatures, feature) => {
  if (Object.keys(feature) in allFeatures) {
    allFeatures = [allFeatures[Object.keys(feature)]].concat(feature);
  } else {
    allFeatures.push(feature);
  }
  return allFeatures;
}, [])

The result of this is:

[{
  "Fabric": ["100% Cotton", 28214]
}, {
  "Cut": ["Skinny", 28214]
}, {
  "Fabric": ["Canvas", 28212]
}, {
  "Buttons": ["Brass", 28212]
}]

This is pretty close to what I am looking for, where I have an array of objects that contain information about the feature and product id of the product, but the repeat in "Fabric" is something I'm struggling to sort out. Ideally, the result would look like this:

[{
  "Fabric": ["100% Cotton", 28214],
  ["Canvas", 28212]
}, {
  "Cut": ["Skinny", 28214]
}, {
  "Buttons": ["Brass", 28212]
}]

If anyone can help guide me as to how to change my formatting function to accomplish this, I'd be very grateful. Alternatively, if anyone knows a better way to dynamically format a table with a single row for each unique feature given my current result, that would be great too.

The data coming into my helper function is as follows:

CurrentProd:

{
  "id": 28212,
  "name": "Camo Onesie",
  "slogan": "Blend in to your crowd",
  "description": "The So Fatigues will wake you up and fit you in. This high energy camo will have you blending in to even the wildest surroundings.",
  "category": "Jackets",
  "default_price": "140.00",
  "created_at": "2021-07-10T17:00:03.509Z",
  "updated_at": "2021-07-10T17:00:03.509Z",
  "features": [{
    "feature": "Fabric",
    "value": "Canvas"
  }, {
    "feature": "Buttons",
    "value": "Brass"
  }]
}

ClickedProd:

{
  "name": "Morning Joggers",
  "category": "Pants",
  "originalPrice": "40.00",
  "salePrice": null,
  "photo": "https://images.unsplash.com/photo-1552902865-b72c031ac5ea?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=300&q=80",
  "id": 28214,
  "features": [{
    "feature": "Fabric",
    "value": "100% Cotton"
  }, {
    "feature": "Cut",
    "value": "Skinny"
  }]
}
reactjs reduce dictionary arrays javascript
3 Answers

There seems to be a bigger question of how to structure your data. You say that ideally your results would look like:

[
  {
    "Fabric":
      ["100% Cotton",28214],
      ["Canvas",28212]
  },
  {
    "Cut":
      ["Skinny",28214]
  },
  {
    "Buttons":
      ["Brass",28212]
  }
]

But what you're really trying to get out of this is a combined list of rows and associated values for each item feature, if it exists. All you really need then is an array of keys for each row you want to display, and objects that let you access the needed property by that key.

The array of keys could look like this:

["Fabric", "Cut", "Buttons"]

The objects you want to access the properties using those keys, for example your CurrentProd, could be this (notice that you can access a feature by calling CurrentProd.features["FeatureName"]):

{
  "id":28212,
  "name":"Camo Onesie",
// ... //
  "features":  {
    "Fabric": "Canvas",
    "Buttons": "Brass"
  }
}

Having said that, to get those things you can get the array of keys, which we'll call allFeatureKeys, by reducing over a combined array of CurrentProd.features and ClickedProd.features:

const allFeatureKeys = [
    ...CurrentProd.features,
    ...ClickedProd.features
  ].reduce((acc, cur) => {
      return acc.findIndex(cur.feature) > -1 ? [...acc, cur.feature] : acc
    },
    []
  );

And you can modify your CurrentProd to the above data shape by reducing over the array of its features, let's call this modifiedCurrentProd:

const modifiedCurrentProd = {
  ...CurrentProd,
  features: CurrentProd.features.reduce((acc, cur) => {
    return {...acc, [cur.feature]: cur.value} 
  }, {})
}

Repeat that for a modifiedClickedProd object, then you have both CurrentProd.features and ClickedProd.features values available for a lookup when you create your table values.

As an example only, since I don't know your react structure or what data you want to display, you can then render the values in the table rows mapping over the keys to make each row, and for each feature key, you access the value from the modifiedCurrentProd or modifiedClickedProd object's features property:

  <div id="table">
    {allFeatureKeys.map((featureKey) => {
       return <div id="table-row">
         <div>{featureKey}</div>
         <div>
           { 
             modifiedCurrentProd.features[featureKey] !== undefined 
               ? modifiedCurrentProd.id 
               : "n/a"
           }
         </div>
         <div>
           {
             modifiedClickedProd.features[featureKey] !== undefined
               ? modifiedClickedProd.id
               : "n/a"
           }
         </div>
       </div>
     })}
  </div>
user_54021690

Firstly the target data structure needs to be fixed/optimized. It looks like the OP does concentrate on something which is based on a generic Feature (like Fabric, Cut, Buttons) whereas such feature values seem to be associated more with the Product. Thus for one and the same feature the values are unique to the product feature. In order to not loose the product information, a target format's feature item needs to reflect its related product's id property.

A viable and still flexible enough target data structure then might look like this ...

{
  "Fabric": [{
    productId: 28214,
    value: "100% Cotton",
  }, {
    productId: 28212,
    value: "Canvas",
  }],
  "Cut": [{
    productId: 28214,
    value: "Skinny",
  }],
  "Buttons": [{
    productId: 28212,
    value: "Brass",
  }],
}

Any approach should start with a data-normalizing mapping-process of a product's features list where each feature item will get its product related id assigned.

Thus a feature item like { feature: "Buttons", value: "Brass" } gets mapped temporarily into { productId: 28212, feature: "Buttons", value: "Brass" }.

The two normalized data-item lists now can be concatenated and finally processed/reduced into the final target structure ...

function mergeBoundProductId(item) {
  return { ...this, ...item };
}
function aggregateProductFeatureValueLists(index, productFeature) {
  const { feature, ...featureValue } = productFeature;
  const featureList = index[feature] ??= [];
  //const featureList = index[feature] || (index[feature] = []);

  featureList.push(featureValue);

  return index;
}

function createIndexOfProductFeatureValues(clickedProd, currentProd) {
  const { features:clickedFeatures } = clickedProd;
  const { features:currentFeatures } = currentProd;

  return [

    ...clickedFeatures.map(mergeBoundProductId, { productId: clickedProd.id }),
    ...currentFeatures.map(mergeBoundProductId, { productId: currentProd.id }),

  ].reduce(aggregateProductFeatureValueLists, {});
}

const currentProduct = {
  id: 28212,
  name: "Camo Onesie",
  // ... more properties ...
  features: [{
    feature: "Fabric",
    value: "Canvas",
  }, {
    feature: "Buttons",
    value: "Brass",
  }],
};
const clickedProduct = {
  name: "Morning Joggers",
  // ... more properties ...
  id: 28214,
  features: [{
    feature: "Fabric",
    value: "100% Cotton",
  }, {
    feature: "Cut",
    value: "Skinny",
  }],
};

console.log(
  'createIndexOfProductFeatureValues(clickedProduct, currentProduct) ...',
  createIndexOfProductFeatureValues(clickedProduct, currentProduct)
);
.as-console-wrapper { min-height: 100%!important; top: 0; }

The advantage of breaking the code into dedicated processes comes with easier refactoring for e.g. changed target structures like something closer to what the OP was looking for.

The changes to the reducer function are minimal. It's just two changes, each barely noticeable in its line ...

function mergeBoundProductId(item) {
  return { ...this, ...item };
}
function aggregateProductFeatureValueLists(index, productFeature) {
  const { feature, productId, value } = productFeature;
  const featureList = index[feature] ??= [];

  featureList.push([value, productId]);

  return index;
}

function createIndexOfProductFeatureValues(clickedProd, currentProd) {
  const { features:clickedFeatures } = clickedProd;
  const { features:currentFeatures } = currentProd;

  return [

    ...clickedFeatures.map(mergeBoundProductId, { productId: clickedProd.id }),
    ...currentFeatures.map(mergeBoundProductId, { productId: currentProd.id }),

  ].reduce(aggregateProductFeatureValueLists, {});
}

console.log(
  'createIndexOfProductFeatureValues(clickedProduct, currentProduct) ...',
  createIndexOfProductFeatureValues(clickedProduct, currentProduct)
);
.as-console-wrapper { min-height: 100%!important; top: 0; }
<script>
  const currentProduct = {
    id: 28212,
    name: "Camo Onesie",
    // ... more properties ...
    features: [{
      feature: "Fabric",
      value: "Canvas",
    }, {
      feature: "Buttons",
      value: "Brass",
    }],
  };
  const clickedProduct = {
    name: "Morning Joggers",
    // ... more properties ...
    id: 28214,
    features: [{
      feature: "Fabric",
      value: "100% Cotton",
    }, {
      feature: "Cut",
      value: "Skinny",
    }],
  };
</script>

The last example's purpose too is to prove the advantage of an easy to refactor code base.

Here the main function gets renamed from createIndexOfProductFeatureValues to createListOfProductFeatureValues.

It's implementation also changes likewise but only in the way how the reducer function gets invoked with its initial value.

The reducer function also does not change dramatically, only in the way of how the accumulating/aggregating collector object gets handled.

And the result is a clean array based object structure ...

function mergeBoundProductId(item) {
  return { ...this, ...item };
}
function aggregateProductFeatureValueLists(collector, productFeature) {
  const { feature, productId, value } = productFeature;
  const { index, list } = collector;
  const featureItem = index[feature] ??= { feature, values: [] };

  if (featureItem.values.length === 0) {
    list.push(featureItem);
  }
  featureItem.values.push([value, productId]);

  return collector;
}

function createListOfProductFeatureValues(clickedProd, currentProd) {
  const { features:clickedFeatures } = clickedProd;
  const { features:currentFeatures } = currentProd;

  return [

    ...clickedFeatures.map(mergeBoundProductId, { productId: clickedProd.id }),
    ...currentFeatures.map(mergeBoundProductId, { productId: currentProd.id }),

  ].reduce(aggregateProductFeatureValueLists, { index: {}, list: [] }).list;
}

console.log(
  'createListOfProductFeatureValues(clickedProduct, currentProduct) ...',
  createListOfProductFeatureValues(clickedProduct, currentProduct)
);
.as-console-wrapper { min-height: 100%!important; top: 0; }
<script>
  const currentProduct = {
    id: 28212,
    name: "Camo Onesie",
    // ... more properties ...
    features: [{
      feature: "Fabric",
      value: "Canvas",
    }, {
      feature: "Buttons",
      value: "Brass",
    }],
  };
  const clickedProduct = {
    name: "Morning Joggers",
    // ... more properties ...
    id: 28214,
    features: [{
      feature: "Fabric",
      value: "100% Cotton",
    }, {
      feature: "Cut",
      value: "Skinny",
    }],
  };
</script>

user_26272430

You are already looping through both once. You can get it without reducing.

const formatFeatures = (currentProd, clickedProd) => {
  const formattedFeatures = {};

  if (clickedProd.features) {
    clickedProd.features.forEach(feature => {
      const vals = Object.values(feature);

      if (!formattedFeatures.hasOwnProperty(vals[0])) {
        formattedFeatures[vals[0]] = [];
      }
      formattedFeatures[vals[0]].push([vals[1], clickedProd.id]);
    });
  }

  currentProd.features.forEach(feature => {
    const vals = Object.values(feature);

    if (!formattedFeatures.hasOwnProperty(vals[0])) {
      formattedFeatures[vals[0]] = [];
    }
    formattedFeatures[vals[0]].push([vals[1], currentProd.id]);
  })

  return formattedFeatures;
}

const currentProd = {
  "id": 28212,
  "name": "Camo Onesie",
  "slogan": "Blend in to your crowd",
  "description": "The So Fatigues will wake you up and fit you in. This high energy camo will have you blending in to even the wildest surroundings.",
  "category": "Jackets",
  "default_price": "140.00",
  "created_at": "2021-07-10T17:00:03.509Z",
  "updated_at": "2021-07-10T17:00:03.509Z",
  "features": [{
    "feature": "Fabric",
    "value": "Canvas"
  }, {
    "feature": "Buttons",
    "value": "Brass"
  }]
};
const clickedProd = {
  "name": "Morning Joggers",
  "category": "Pants",
  "originalPrice": "40.00",
  "salePrice": null,
  "photo": "https://images.unsplash.com/photo-1552902865-b72c031ac5ea?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=300&q=80",
  "id": 28214,
  "features": [{
    "feature": "Fabric",
    "value": "100% Cotton"
  }, {
    "feature": "Cut",
    "value": "Skinny"
  }]
};
console.log(formatFeatures(currentProd, clickedProd));
.as-console-wrapper { min-height: 100%!important; top: 0; }

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