Question 245669 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – combining data from two objects

do you know how to get array like this

[
    {
        index: 4,
        years: [1999, 2001, 2012, 2020, 1999, 1998, 2020],
        price: 200
    },
    {
        index: 2,
        years: [1999, 2019, 2020],
        price: 0
    },
        {
        index: 3,
        years: [2020, 1999, 2019, 2020],
        price: 100
    }
]

with this data

[
    {
        index: 4,
        years: [1999, 1998, 2020],
        price: 100
    },
    {
        index: 4,
        years: [1999, 2001, 2012, 2020],
        price: 200
    },
    {
        index: 2,
        years: [1999, 2019, 2020],
        price: 0
    },
    {
        index: 3,
        years: [1999, 2019, 2020],
        price: 0
    },
    {
        index: 3,
        years: [2020],
        price: 100
    }
    
]

I would like to get the highest price value for the same index and connect the year arrays.

I have no idea how to get such a result.

Tags:

2

Answers


  1. 0

    Collect items with the same index in a map. If an item with a bigger price is found, replace the previous item. If the price is the same merge the years with a set:

    const result = [...arr.reduce((map, item) => {
  const found = map.get(item.index);
  if(!found || found.price < item.price){
      map.set(item.index, item);
  } else if (found.price === item.price){ // merge years
      found.years = [...new Set([...found.years, ...item.years])];
  }
  return map;
}, new Map).values()];

console.log(result);
    <script>
const arr = [
    {
        index: 4,
        years: [1999, 2001, 2012, 2020, 1999, 1998, 2020],
        price: 200
    },
    {
        index: 2,
        years: [1999, 2019, 2020],
        price: 0
    },
        {
        index: 3,
        years: [2020, 1999, 2019, 2020],
        price: 100
    },
    {
        index: 4,
        years: [1999, 1998, 2020],
        price: 100
    },
    {
        index: 4,
        years: [1999, 2001, 2012, 2020],
        price: 200
    },
    {
        index: 2,
        years: [1999, 2019, 2020],
        price: 0
    },
    {
        index: 3,
        years: [1999, 2019, 2020],
        price: 0
    },
    {
        index: 3,
        years: [2020],
        price: 100
    }
]
</script>
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  2. 0

    I created a custom reducer below that accepts an accessor (key or function); a reducer function that takes the existing value, and the current value; and a dataArr (array of item arrays). The first object has priority, so only its price will update.

    const main = () => {
  const accessor = ({ index }) => index; // or simply 'index'
  const reducer = (existing, item) => {
    existing.price = Math.max(existing.price, item.price);
    return existing;
  };
  const c = combine(accessor, reducer, a, b);
  console.log(c.map(item => JSON.stringify(item)).join('n'));
};

const combine = (accessor, reducer, ...dataArr) => {
  const lookup = new Map();
  for (const data of dataArr) {
    for (let item of data) {
      const k = accessor instanceof Function ? accessor(item) : item[accessor];
      const existing = lookup.get(k);
      lookup.set(k, existing ? reducer(existing, item) : structuredClone(item));
    }
  }
  return [...lookup.values()];
};

const a = [{
  index: 4,
  years: [1999, 2001, 2012, 2020, 1999, 1998, 2020],
  price: 200
}, {
  index: 2,
  years: [1999, 2019, 2020],
  price: 0
}, {
  index: 3,
  years: [2020, 1999, 2019, 2020],
  price: 100
}];

const b = [{
  index: 4,
  years: [1999, 1998, 2020],
  price: 100
}, {
  index: 4,
  years: [1999, 2001, 2012, 2020],
  price: 200
}, {
  index: 2,
  years: [1999, 2019, 2020],
  price: 0
}, {
  index: 3,
  years: [1999, 2019, 2020],
  price: 0
}, {
  index: 3,
  years: [2020],
  price: 100
}];

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