Grouping array of objects by multiple keys

Question

I feel embarrassed for asking this question as I should know how to figure it out, but I'm spinning my wheels on grouping an array of objects by multiple keys.

Here's the data:

[
      {
        "car": "audi",
        "type": "A6",
        "style": "Avant",
        "year": "1996"
      },
      {

        "car": "audi",
        "type": "A4",
        "style": "2",
        "year": "2006"
      },
      {

        "car": "audi",
        "type": "A4",
        "style": "L W12",
        "year": "2006"
      },
      {

        "car": "audi",
        "type": "80",
        "style": "GLE",
        "year": "1975"
      },
      {

        "car": "audi",
        "type": "A6",
        "style": "Avant L",
        "year": "1996"
      },
      {
        "car": "audi",
        "type": "A6",
        "style": "3.2 Multitronic",
        "year": "2006"
      },
]

What I've been trying to generate with little success is the following:

 [{
   "audi": [{
     "1996": {
       "A6": ["Avant, Avant L"]
     }
   }, {
     "2006": }
       "A6": ["3.2 Multitronic"],
       "A4": ["L W12", "2"]
     }
   }
   ....
 }]

The schema is:

{
    "car1": [{
        "year1": {
            "style1": ["trim1", "trim2"],
            "style2": ["trim1", "trim2"]
        },
        "year1": {
            "style1": ["trim1", "trim2"],
            "style2": ["trim1", "trim2"]
        }
    }],
    "car2": [{
        "year1": {
            "style1": ["trim1", "trim2"],
            "style2": ["trim1", "trim2"]
        },
        "year2": {
            "style1": ["trim1", "trim2"],
            "style2": ["trim1", "trim2"]
        }
    }]
}

I've tried the following with lodash

  let result = _.chain(carData)
    .groupBy('car')
    .toPairs()
    .map(function(curr) {
        return _.zipObject(['car', 'year'], curr);
    })
    .value();

This gets me part of the way, but I end up with incomplete data when it comes to the styles and types for each year of the car.

please add your attempt.

Nina Scholz
– Nina Scholz

2017-02-24 21:48:30 +00:00
Commented Feb 24, 2017 at 21:48 — Nina Scholz
– Nina Scholz, Commented Feb 24, 2017 at 21:48
Updated, but I'm trying not to use lodash in this case

hybrid9
– hybrid9

2017-02-24 22:00:18 +00:00
Commented Feb 24, 2017 at 22:00 — hybrid9
– hybrid9, Commented Feb 24, 2017 at 22:00

Nina Scholz · Accepted Answer · 2017-02-24 22:23:26Z

2

You could use a hash object and a nested approach for the given properties.

var data = [{ car: "audi", type: "A6", style: "Avant", year: 1996 }, { car: "audi", type: "A4", style: 2, year: 2006 }, { car: "audi", type: "A4", style: "L W12", year: 2006 }, { car: "audi", type: 80, style: "GLE", year: 1975 }, { car: "audi", type: "A6", style: "Avant L", year: 1996 }, { car: "audi", type: "A6", style: "3.2 Multitronic", year: 2006 }],
    keys = ['car', 'year', 'type'],
    result = [];

data.forEach(function (a) {
    keys.reduce(function (r, k) {
        var o = {};
        if (!r[a[k]]) {
            r[a[k]] = { _: [] };
            o[a[k]] = r[a[k]]._;
            r._.push(o);
        }
        return r[a[k]];
    }, this)._.push(a.style);
}, { _: result });
   
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Feb 24, 2017 at 22:23

answered Feb 24, 2017 at 22:17

Nina Scholz

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2 Comments

hybrid9 Over a year ago

My mind is blown. Would you mind stepping through your code a bit? I'm especially curious about the { _: result } being passed in as the initial value for reduce().

Nina Scholz Over a year ago

actually this method is basically as similar as Convert an array of json objects in to another json object, where just the keys are easier to access and the result is easier created without callback. for the hash table, you get an insight of the methods and the grouping capabilities.

Rares Matei · Accepted Answer · 2017-02-24 22:50:01Z

Here's a (slightly verbose) solution that generates exactly the JSON object shape you wanted and groups by unlimited keys:

var cars = [{
  "car": "audi",
  "type": "A6",
  "style": "Avant",
  "year": "1996"
}, {

  "car": "audi",
  "type": "A4",
  "style": "2",
  "year": "2006"
}, {

  "car": "audi",
  "type": "A4",
  "style": "L W12",
  "year": "2006"
}, {

  "car": "audi",
  "type": "80",
  "style": "GLE",
  "year": "1975"
}, {

  "car": "audi",
  "type": "A6",
  "style": "Avant L",
  "year": "1996"
}, {
  "car": "audi",
  "type": "A6",
  "style": "3.2 Multitronic",
  "year": "2006"
}, ];

function groupBy(list, prop) {
  return list.reduce((groupped, item) => {
    var key = item[prop];
    delete item[prop];
    if (groupped.hasOwnProperty(key)) {
      groupped[key].push(item);
    } else {
      groupped[key] = [item];
    }
    return groupped
  }, {});
}

function groupSubKeys(obj, properties, propIndex) {
  var grouppedObj = groupBy(obj, properties[propIndex]);
  Object.keys(grouppedObj).forEach((key) => {
    if (propIndex < properties.length - 2) {
      grouppedObj[key] = groupSubKeys(grouppedObj[key], properties, propIndex + 1);
    } else {
      grouppedObj[key] = grouppedObj[key].map(item => item[properties[propIndex + 1]])
    }
  });
  return grouppedObj;
}

function groupByProperties(list, properties) {
  return groupSubKeys(list, properties, 0);
}

console.log(groupByProperties(cars, ['car', 'year', 'type', 'style']));

Here's a running example: http://codepen.io/rarmatei/pen/evmBOo

This one looks great too. I couldn't get my head wrapped around grouping by subKeys and would end up with empty arrays. I appreciate the time you provided to put this together.

Amr Omar · Accepted Answer · 2022-06-26 21:09:55Z

const groupBy = function groupBy(list, properties, propertyIndex)  {
      // current property index
      let i = propertyIndex === undefined ? 0 : propertyIndex;
    
      // group by
      let grouppedObj = list.reduce((acc, obj) => {
        let groupedValue = obj[properties[i]];
        if (!groupedValue) {
          return acc;
        }
        if (!acc[groupedValue]) {
          acc[groupedValue] = [];
        }
        acc[groupedValue].push({ ...obj, groupBy: properties.join(",") });
        return acc;
      }, {});
    
      // group by nested
      const keys = Object.keys(grouppedObj);
      if (i === properties.length - 1) {
        return grouppedObj;
      }
      keys.forEach((key) => {
        grouppedObj[key] = groupBy(grouppedObj[key], properties, i + 1);
      });
      return grouppedObj;
    };
    
    const data =[
  {
    "year": "2021",
    "cabin": "1",
    "months": ["1", "2"]
  },
  {
    "year": "2021",
    "cabin": "1",
    "months": ["4"]
  },
  {
    "year": "2021",
    "cabin": "2",
    "months": ["1", "2"]
  },
  {
    "year": "2022",
    "cabin": "1",
    "months": ["1", "2"]
  },
  {
    "year": "2022",
    "cabin": "1",
    "months": ["4"]
  },
  {
    "year": "2022",
    "cabin": "2",
    "months": ["1", "2"]
  }
];

 const results=groupBy(data, ["year", "cabin"]);
console.log(results);

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