adding up the value of an array with another array - arrays

Question

can I get the sum of amount if I have an array like the one below?
[{"_id":"5e154cf38c52231ee19f8",
"refunds":[
{"_id":"5e38f10a754fcf3d48015",
"reason":"refund 1",
"amount":50000,
]},
{"_id":"5e1578b48c52231ee19f8",
"refunds":[
{"_id":"5e37e09ef9ea5e3784043",
"reason":"refund 1",
"amount":100000,
{"_id":"5e37e12a02c27c14580a1",
"reason":"refund 2",
"amount":100000,
{"_id":"5e38f02b754fcf3d48015",
"reason":"refund 3",
"amount":50000,
]},
{"_id":"5e1578b48c52231ee19f8",
"refunds":[]
}]
I hope to get res = 300000

Answer 1

This should be relatively straightforward, we create a flat array of all refund objects using flatMap, then we'll use reduce to sum the total amount.
I've added another function, sumRefundAmountsII to workaround JavaScript environments that do not support.flatMap (pre ES2019)
const data = [ { "_id": "5e154cf38c52231ee19f8", "refunds": [ { "_id": "5e38f10a754fcf3d48015", "reason": "refund 1", "amount": 50000 } ] }, { "_id": "5e1578b48c52231ee19f8", "refunds": [ { "_id": "5e37e09ef9ea5e3784043", "reason": "refund 1", "amount": 100000 }, { "_id": "5e37e12a02c27c14580a1", "reason": "refund 2", "amount": 100000 }, { "_id": "5e38f02b754fcf3d48015", "reason": "refund 3", "amount": 50000 } ] }, { "_id": "5e1578b48c52231ee19f8", "refunds": [] }];
function sumRefundAmounts(array) {
// Get an array of all refunds.
const refunds = array.flatMap(obj => obj.refunds);
// Sum amount for each refund.
return refunds.reduce((sum, refund) => {
return sum + refund.amount;
}, 0);
}
console.log("Total amount:", sumRefundAmounts(data));
// Use this function if your JavaScript environment complains about .flatMap
function sumRefundAmountsII(array) {
// Use a work around if we don't have flatMap...
const refunds = [].concat.apply([], array.map(obj => obj.refunds));
// Sum amount for each refund.
return refunds.reduce((sum, refund) => {
return sum + refund.amount;
}, 0);
}
console.log("Total amount (no flat map):", sumRefundAmountsII(data));

Answer 2

Before answering ... I assume 2 things -
1st - you are looking answer in the Java. 2nd - And you can do things much easier way in java List :
Let we make 2 classes Refund & Composite (Containing List)-
Refund Class -
package com.sabre.ticketing.dhs.service.create.domain;
public class Refund {
String _id;
String reason;
int amount;
public Refund(String _id, String reason, int amount) {
this._id = _id;
this.reason = reason;
this.amount = amount;
}
public int getAmount() {
return amount;
}
}
And here is Composite Class as -
package com.sabre.ticketing.dhs.service.create.domain;
import java.util.List;
public class Composite {
String _id;
List<Refund> refunds;
public Composite(String _id, List<Refund> refunds) {
this._id = _id;
this.refunds = refunds;
}
public List<Refund> getRefunds() {
return refunds;
}
}
The calculation technique is in SumCalc class -
package com.sabre.ticketing.dhs.service.create.domain;
import java.util.ArrayList;
import java.util.List;
public class SumCalc {
public static void main(String[] args){
List<Composite> composites = List.of(new Composite("5e154cf38c52231ee19f8", List.of(new Refund("5e38f10a754fcf3d48015", "refund 1", 50000))),
new Composite("5e154cf38c52231ee19f8",
List.of(new Refund("5e37e09ef9ea5e3784043", "refund 1", 100000),
new Refund("5e37e12a02c27c14580a1", "refund 2", 100000),
new Refund("5e38f02b754fcf3d48015", "refund 3", 50000))),
new Composite("5e154cf38c52231ee19f8", new ArrayList<>()));
// Basically get you Json converted into composites list.. for simplicity and dont want to jackson thing i have initialized list as new ..
Integer finalSum = composites.stream()
.map(Composite::getRefunds)
.flatMap(List::stream)
.map(Refund::getAmount)
.reduce((sum, val) -> sum + val)
.orElse(0);
System.out.println("final Sum is " + finalSum);
}
}
Run the SumClac ...
final Sum is 300000
Process finished with exit code 0