How to the get the sum of all the field with the same name in a nested array?

Question

I'm trying to find the sum of all the field values of the nested array, I suck at explaining stuffs like this, I hope the code below will give you some insight of what I want to do.

The array looks like this

data = [
    {
        id: 8434,
        name: listName, 
        data: [
            {name: "a name",
             quantity: 20,
            }
            {name: "another name",
             quantity: 40,
            }
            {name: "another new name",
             quantity: 40,
            }
        ]
    }, 
    {
        id: 54343,
        name: "new list name", 
        data: [
            {name: "a name",
             quantity: 12,
            }
            {name: "another name",
             quantity: 10,
            }
            {name: "another new name",
             quantity: 16,
            }
        ]
    }
]

This is how I want the data to be after carrying out the sum

transformed = [
{name: "a name", quantity: 32},
{name: "another name", quantity: 50},
{name: "another new name", quantity: 56}
]

Answer 1

You can use Array.flatMap() followed by Array.reduce() to get the desired result.

We start by calling .flatMap() to get all the data values, then calling .reduce() on these to sum each value by name .

This will create an object, with a property for each name, we then call Object.values() to return to an array.

 const data = [ { id: 8434, name: 'listName', data: [ { name: "a name", quantity: 20, }, { name: "another name", quantity: 40, }, { name: "another new name", quantity: 40, } ] }, { id: 54343, name: "new list name", data: [ { name: "a name", quantity: 12, }, { name: "another name", quantity: 10, }, { name: "another new name", quantity: 16, } ] } ]; const transformed = Object.values(data.flatMap(({ data }) => data).reduce((acc, { name , quantity }) => { acc[name] = acc[name] || { name, quantity: 0 }; acc[name].quantity += quantity; return acc; }, {})) console.log('Transformed:', transformed)

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Answer 2

const transform = (data) => {
  const quantitySum = new Map()
  
  data.forEach(list => {
    list.data.forEach(({ name, quantity }) => {
      if (quantitySum.has(name)) {
        quantitySum.set(name, quantitySum.get(name) + quantity)
      } else {
        quantitySum.set(name, quantity)
      }
    })
  })
  
  return Array.from(quantitySum.entries())
    .map(([name, sum]) => ({
    name,
    quantity: sum
  }))
}

Answer 3

just loop them through and create a new object..

const data = [
    {
        id: 8434,
        name: 'listName', 
        data: [
            {
                name: "a name",
                quantity: 20,
            },
            {
                name: "another name",
                quantity: 40,
            },
            {
                name: "another new name",
                quantity: 40,
            }
        ]
    }, 
    {
        id: 54343,
        name: "new list name", 
        data: [
            {
                name: "a name",
                quantity: 12,
            },
            {
                name: "another name",
                quantity: 10,
            },
            {
                name: "another new name",
                quantity: 16,
            }
        ]
    }
]


// Logic:
const transformed = []

data.forEach(d => {
    d.data.forEach(item => {
        const exist = transformed.find(t => t.name == item.name)
        if(exist) 
            exist.quantity += item.quantity
        else 
            transformed.push(item)
    })
})

console.log(transformed)

Output:

[
  { name: 'a name', quantity: 32 },
  { name: 'another name', quantity: 50 },
  { name: 'another new name', quantity: 56 }
]