In a javascript object, how to sum values from one field if a tag exists in another field?

user_15614220 0
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If the data is like: -

const dis ={
    "data":[
        {
            "Hazard_type": ["Tornado","Hurricane"],
            "County": "Anderson",
            "State": "TX",
            "FIPS_code": 48001,
            "Longitude": -95.687072,
            "Latitude": 31.776143,
            "Property_Damage": 10000000,
            "Crop_Damage": 0
        },
        {
            "Hazard_type": ["Hurricane"],
            "County": "Anderson",
            "State": "TX",
            "FIPS_code": 48001,
            "Longitude": -95.687072,
            "Latitude": 31.776143,
            "Property_Damage": 4914933.84,
            "Crop_Damage": 0
        },
    ]
}

And I want to create another json array which has aggregate damage per unique tag in the Hazard type. What should be the approach here? (Very new to Javascript)

javascript
2 Answers

You can use the Array.map function. See the definition for this function here:

For example, you can use it for:

const rows = [
  { name: "Name 1", price: 1.0, tax, 0.5 }, 
  { name: "Name 2"price: 2.0, tax, 0.5 }
];
const newRows = rows.map(row => {
   return {
      ..row,
      totalPrice: row.price + tax,
   };
});

So after of this newRows is like:

[
  { name: "Name 1", price: 1.0, tax, 0.5, totalPrice: 1.5 }, 
  { name: "Name 2"price: 2.0, tax, 0.5, totalPrice: 2.5 }
]
user_81767170

Here's one way you might accomplish the task, making use of Array.filter and Array.reduce.

Note that I changed the values of Crop_Damage from zeros to 3 and 1, to make it more evident the code works.

const dis ={
    "data":[
        {
            "Hazard_type": ["Tornado","Hurricane"],
            "County": "Anderson",
            "State": "TX",
            "FIPS_code": 48001,
            "Longitude": -95.687072,
            "Latitude": 31.776143,
            "Property_Damage": 10000000,
            "Crop_Damage": 1
        },
        {
            "Hazard_type": ["Hurricane"],
            "County": "Anderson",
            "State": "TX",
            "FIPS_code": 48001,
            "Longitude": -95.687072,
            "Latitude": 31.776143,
            "Property_Damage": 4914933.84,
            "Crop_Damage": 3
        },
    ]
};

const removeDuplicates = (key, index, array) => {
  return array.lastIndexOf(key) === index;
};

const distinctHazards = dis.data.map(row => row.Hazard_type).flat().filter(removeDuplicates);

/*
 * Array.filter() ensures we only examine the subset of the array having to do with one Hazard at a time
 * Array.reduce() is an accumulator that simply sums the fields (Crop_Damage) up. 
*/
const scores = distinctHazards.map(hazard => {
    const damages = dis.data.filter(row => {
        return row.Hazard_type.includes(hazard);
    });
    return {hazard, damages: damages.map(row => row.Crop_Damage).reduce((a,b) => {
        return Number(a) + Number(b);
    })};
});

console.log(scores);

user_9770830
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