Map Reduce/Sum using Underscorejs - json

Question

I am trying to convert the following dataset:
var data = {
"csrf": "token",
"items": [
{"category": "product1", "image": "image1.jpg", "cost": "$6", "item_totals": [
{"category": "discount", "amount": "-$1.0"}]
},
{"category": "product2", "image": "image2.jpg", "cost": "$8", "item_totals": [
{"category": "discount", "amount": "-$1.2"}]
}],
"totals": [
{"category": "shipping", "amount": "$0.00", "name": "Shipping", "is_zero": true},
{"category": "taxes", "amount": "$0.00", "name": "Taxes", "is_zero": true}
],
"total": "$1234", "subtotal": "$1234", "id": abc123, "currency_code": "USD"}
into a single value, being the sum of all 'amount' values in the item_totals array(s). I cannot seem to do this whilst accounting a varying amount of records in 'items' & for empty 'item_total' arrays. Any help would be great!

Answer 1

var data = {
"csrf": "token",
"items": [{
"category": "product1",
"image": "image1.jpg",
"cost": "$6",
"item_totals": [{
"category": "discount",
"amount": "-$1.0"
}]
},
{
"category": "product2",
"image": "image2.jpg",
"cost": "$8",
"item_totals": [ // multiple item_totals
{
"category": "discount",
"amount": "-$1.2"
},
{
"category": "discount",
"amount": "-$1.2"
}
]
},
{
"category": "product2",
"image": "image2.jpg",
"cost": "$8",
"item_totals": [] // empty item_totals
},
{
"category": "product2",
"image": "image2.jpg",
"cost": "$8"
// absent item_totals
}
],
"totals": [{
"category": "shipping",
"amount": "$0.00",
"name": "Shipping",
"is_zero": true
},
{
"category": "taxes",
"amount": "$0.00",
"name": "Taxes",
"is_zero": true
}
],
"total": "$1234",
"subtotal": "$1234",
"id": "abc123",
"currency_code": "USD"
}
var totalAmount = _.chain(data.items)
.map(item => item.item_totals || []) // emit totals
.tap(console.log)
.reduce((memo, bucket) => memo.concat(bucket), []) // collect (flatten)
.tap(console.log)
.map(total => parseFloat(total.amount.replace('$', ''), 10)) // emit amounts
.tap(console.log)
.reduce((ret, amount) => ret + amount, 0) // collect (sum)
.value();
console.log(totalAmount);
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