sum a field value in an object array

Question

Grabbing data from a csv file then assigning to an object array, SmartPostShipments []. Outputting the "total" number of elements in the array is pretty straightforward by using the .length property, but I also need to get the sum of each field value in the object array called ['Net Charge Amount']. What is the best way to accomplish this? I am fine with using console.log() for this illustration.

const { parse } = require('csv-parse')
const fs = require('fs')
const SmartPostShipments = []

function isSmartpost(shipment) {
    return shipment['Service Type'] === 'SmartPost'
}

fs.createReadStream('test.csv')
    .pipe(parse({
        columns: true
    }))
    
    .on('data', (data) => {
        if (isSmartpost(data)) {
            SmartPostShipments.push(data)
        }

 })
    .on('error', (err) => {
        console.log(err)
    })

 .on ('end', () => {
        
    // This outputs each individual 'net charge amount', but how do I just display the sum 
    // total?
    
    console.log(SmartPostShipments.map((shipment)=> {
            return shipment['Net Charge Amount']
        }))
        
       console.log(`${SmartPostShipments.length} Smartpost shipments.`)
     
    })

A couple of the code suggestions look good, but the data is appending instead of summing. Here's a pic of the output:

 console.log(SmartPostShipments.map((shipment)=> {
        return shipment['Net Charge Amount']
    }))
            
    const sum = SmartPostShipments.reduce((partialSum, shipment) => partialSum + shipment['Net Charge Amount'], 0)
    console.log(sum)

    const sumSP = SmartPostShipments.reduce((cur, pre)=> {
        return cur+=pre['Net Charge Amount'];
      },0)
      console.log(sumSP)

Adding parseInt() did the trick: return cur += parseInt(pre['Net Charge Amount']); Total value = 490 — Derek, Feb 13 '23 at 21:29

score 4 · Answer 1 · answered Feb 13 '23 at 20:40

4

This is a variation of this question. Applied to your situation the code would be:

const sum = SmartPostShipments.reduce((partialSum, shipment) => partialSum + shipment['Net Charge Amount'], 0)

answered Feb 13 '23 at 20:40

Austin

41
3

tzztson · Accepted Answer · 2023-02-13T20:52:43.190

2

const sum = SmartPostShipments.reduce((cur, pre)=> {
  return cur+=pre['Net Charge Amount'];
},0)
console.log(sum)

Please try the above. Hope it works.

edited Feb 13 '23 at 20:52

answered Feb 13 '23 at 20:35

tzztson

328
3
22

He's looking for the sum of a property of the objects, I think it would need to be something like `return cur+=pre['Net Charge Amount'];` – mpallansch Feb 13 '23 at 20:37
Thank you, I've just forgot to add that. – tzztson Feb 13 '23 at 20:53

sum a field value in an object array

2 Answers2