ES6 Reduce nested objects in an array

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I've been using map and reduce over some objects and arrays which have been working well so far, however I'm having trouble with one array.

Example of data here:

var arr =
[
[
{
  "id": 6501511,
  "invoiceId": {
    "id": 1043773
  },
  "chargeBandType": "TIME",
  "jobTaskId": {
    "id": 19399852
  },
  "invoicedNet": {
    "amountString": 0,
    "currencyType": "USD"
  },
  "invoicedTaxOneOtherCurrency": null,
  "invoicedTaxOne": {
    "amountString": 0,
    "currencyType": "USD"
  },
  "taxOneRate": 0.1
},
{
  "id": 6501517,
  "invoiceId": {
    "id": 1043773
  },
  "chargeBandType": "TIME",
  "jobTaskId": null,
  "jobExpenseId": null,
  "jobThirdPartyCostId": {
    "id": 20602
  },
  "invoicedNet": {
    "amountString": 0,
    "currencyType": "USD"
  },
  "invoicedTaxOneOtherCurrency": null,
  "invoicedTaxOne": {
    "amountString": 0,
    "currencyType": "USD"
  },
  "taxOneRate": 0.1
},
{
  "id": 6501508,
  "invoiceId": {
    "id": 13773
  },
  "chargeBandType": "TIME",
  "jobTaskId": {
    "id": 19398574
  },
  "invoicedNet": {
    "amountString": 30,
    "currencyType": "USD"
  },
  "invoicedTaxOneOtherCurrency": null,
  "invoicedTaxOne": {
    "amountString": 3,
    "currencyType": "USD"
  },
  "taxOneRate": 0.1
},
{
  "id": 65014,
  "invoiceId": {
    "id": 104
  },
  "chargeBandType": "TIME",
  "jobTaskId": null,
  "jobExpenseId": null,
  "jobThirdPartyCostId": {
    "id": 206
  },
  "invoicedNet": {
    "amountString": 0,
    "currencyType": "USD"
  },
  "invoicedTaxOneOtherCurrency": null,
  "invoicedTaxOne": {
    "amountString": 0,
    "currencyType": "USD"
  },
  "taxOneRate": 0.1
}],
[
{
  "id": 6483,
  "invoiceId": {
    "id": 1042400
  },
  "chargeBandType": "TIME",
  "jobTaskId": {
    "id": 198574
  },
  "invoicedNet": {
    "amountString": 100,
    "currencyType": "USD"
  },
  "invoicedTaxOneOtherCurrency": null,
  "invoicedTaxOne": {
    "amountString": 10,
    "currencyType": "USD"
  },
  "taxOneRate": 0.1
}
]
];

I am trying to reduce the values of invoicedNet.amountString, which would bring a sum of 130 in the case above.

I have tried many ways to work this, including functions similar to the below:

var sum = arr.reduce(function(a, b) {
return a += b.invoicedNet.amountString;
}, 0);

However, no matter how I try this, I keep getting the error:

TypeError: Cannot read property 'amountString' of undefined

(It seems to pick up b.invoicedNet as an object though).

Could anyone suggest an approach to this?

Thanks!

object reduce arrays json javascript
4 Answers
var sum = arr.reduce(function(a, b) {
return a += b.invoicedNet.amountString;
}, 0);

The above code doesn't work because arr is a multidimensional array. Its elements are also an array. You need a nested reducer for this type of array. with the arrow function, it can be written as -

const total = arr.reduce((sum, tasks) => tasks.reduce((previousSum, task) =>
              previousSum + task.invoicedNet.amountString, sum) , 0);
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