How to get correct array sum in array?

Question

We have the following initialDataSet

0: {ID: 1, Province/State: "", Country/Region: "Thailand", Lat: 15, Long: 101, …}
1: {ID: 2, Province/State: "", Country/Region: "Japan", Lat: 36, Long: 138, …}
2: {ID: 3, Province/State: "", Country/Region: "Singapore", Lat: 1.2833, Long: 103.8333, …}
...

Inside each of them We have:

0:
ID: 1
Province/State: ""
Country/Region: "Thailand"
Lat: 15
Long: 101
data: (62) [{…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {

And inside each data: We have:

data: Array(62)
0: {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0}
1: {date: "1/23/20", Confirmed: 3, Deaths: 0, Recovered: 0}
2: {date: "1/24/20", Confirmed: 5, Deaths: 0, Recovered: 0}

And we need to get the total sum of Deaths

We did:

const initialDataSet = [
{ID: 1, "Province/State": "", "Country/Region": "Thailand", Lat: 15, Long: 101, data : [  {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: 0, Recovered: 0},
 {date: "1/24/20", Confirmed: 5, Deaths: 0, Recovered: 0}
]},
 {ID: 2, "Province/State": "", "Country/Region": "Japan", Lat: 36, Long: 138, data : [ {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: 0, Recovered: 0},
 {date: "1/24/20", Confirmed: 5, Deaths: 0, Recovered: 0}
]},
 {ID: 3, "Province/State": "", "Country/Region": "Singapore", Lat: 1.2833, Long: 103.8333, data: [ {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: 0, Recovered: 0},
 {date: "1/24/20", Confirmed: 5, Deaths: 0, Recovered: 0}
]}
];


var testTotals = [];
for (var d = 0; d < initialDataSet.length; d++) {
  var trackObj = initialDataSet[d];
  for (var c = 0; c < trackObj.data.length; c++) {
    testTotals.push(parseInt(trackObj.data[c].Deaths));
  }
}
var myTots = testTotals.reduce((a, b) => a + b, 0);
console.log(myTots);

But console gives NaN

Answer 1

Given the (big) data set that you're working on, the following extra information could be extracted:

1. The time series are incremental, which means that the last value of the data array is the total number at that point in time; this reduces one inner loop
2. If the last value of the data array is an empty string, there's no positive integer preceding it, which means that you can just coerce that value by using || 0

I've adjusted your data set to highlight those findings, and changed the solution accordingly.

const initialDataSet = [
{ID: 1, "Province/State": "", "Country/Region": "Thailand", Lat: 15, Long: 101, data : [  {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: 0, Recovered: 0},
 {date: "1/24/20", Confirmed: 5, Deaths: '', Recovered: 0}
]},
 {ID: 2, "Province/State": "", "Country/Region": "Japan", Lat: 36, Long: 138, data : [ {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: 2, Recovered: 0},
 {date: "1/24/20", Confirmed: 5, Deaths: 3, Recovered: 0}
]},
 {ID: 3, "Province/State": "", "Country/Region": "Singapore", Lat: 1.2833, Long: 103.8333, data: [ {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: 0, Recovered: 0},
 {date: "1/24/20", Confirmed: 5, Deaths: '', Recovered: 0}
]}
];

const x = initialDataSet.reduce((total, {data}) => {
  const lastItem = data[data.length - 1]
  // it's unlikely, but possible that `data` is an empty array
  return lastItem ? total + (lastItem.Deaths || 0) : total
}, 0)
console.log(x);

Answer 2

You could reduce with a nested approach.

const
    initialDataSet = [{ ID: 1, "Province/State": "", "Country/Region": "Thailand", Lat: 15, Long: 101, data: [{ date: "1/22/20", Confirmed: 2, Deaths: '', Recovered: 0 }, { date: "1/23/20", Confirmed: 3, Deaths: 2, Recovered: 0 }, { date: "1/24/20", Confirmed: 5, Deaths: 3, Recovered: 0 }] }, { ID: 2, "Province/State": "", "Country/Region": "Japan", Lat: 36, Long: 138, data: [{ date: "1/22/20", Confirmed: 2, Deaths: 2, Recovered: 0 }, { date: "1/23/20", Confirmed: 3, Deaths: 4, Recovered: 0 }, { date: "1/24/20", Confirmed: 5, Deaths: 5, Recovered: 0 }] }, { ID: 3, "Province/State": "", "Country/Region": "Singapore", Lat: 1.2833, Long: 103.8333, data: [{ date: "1/22/20", Confirmed: 2, Deaths: 1, Recovered: 0 }, { date: "1/23/20", Confirmed: 3, Deaths: 2, Recovered: 0 }, { date: "1/24/20", Confirmed: 5, Deaths: 3, Recovered: 0 }] }]
    total = initialDataSet.reduce((sum, { data }) =>
        data.reduce((s, { Deaths }) => s + (Deaths || 0), sum), 0);

console.log(total);

Answer 3

Add a simple test to your loop:

var testTotals = [];
for (var d = 0; d < initialDataSet.length; d++) {
  var trackObj = initialDataSet[d];
  for (var c = 0; c < trackObj.data.length; c++) {
    testTotals.push(parseInt(trackObj.data[c].Deaths || 0));
  }
}
var myTots = testTotals.reduce((a, b) => a + b, 0);
console.log(myTots);

Note that unless you need the individual values as an array for other reasons, you could do all the math in the initial iteration.

Another thing you could do would be to explicitly convert the value to a number, and then only add the value if it isn't NaN:

var testTotals = [];
for (var d = 0; d < initialDataSet.length; d++) {
  var trackObj = initialDataSet[d];
  for (var c = 0; c < trackObj.data.length; c++) {
    let value = +trackObj.data[c].Deaths;
    if (!isNaN(value))
      testTotals.push(value);
  }
}
var myTots = testTotals.reduce((a, b) => a + b, 0);
console.log(myTots);

That would also handle entries with Deaths: "N/A" or other non-numeric, non-empty strings.

Answer 4

Looks like the data is incremental, so you have to sum just the last ones.
You might do it with reduce.

And to handle NaNs, you might use ~~ (double binary not) which coerce values to integers.

const initialDataSet = [
{ID: 1, "Province/State": "", "Country/Region": "Thailand", Lat: 15, Long: 101, data : [  
 {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: "", Recovered: 0},
 {date: "1/24/20", Confirmed: 5, Deaths: 0, Recovered: 0}
]},
 {ID: 2, "Province/State": "", "Country/Region": "Japan", Lat: 36, Long: 138, data : [
 {date: "1/22/20", Confirmed: 2, Deaths: 'none', Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: "0", Recovered: 0},
 {date: "1/24/20", Confirmed: 5,              Recovered: 0}
]},
 {ID: 3, "Province/State": "", "Country/Region": "Singapore", Lat: 1.2833, Long: 103.8333, data: [
 {date: "1/22/20", Confirmed: 2, Deaths: 0, Recovered: 0},
 {date: "1/23/20", Confirmed: 3, Deaths: 1, Recovered: 0},
 {date: "1/24/20", Confirmed: 5, Deaths: "2", Recovered: 0}
]}
];


var deathsTotals = initialDataSet.reduce((t, {data}) => t + ~~data[data.length-1].Deaths, 0);
  
console.log(deathsTotals)