Sum of one index in multiple arrays using .reduce

Question

The picture below shows the arrays I am pulling from HealthKit's step counter. The arrays have step count values of 33 + 97 + 75.

Image Here

I'm not sure how to grab the second index in each array and add them together to get 205.

I am currently using:

let stepSum = (data as any).reduce((a, b) => a + b.quantity, 0);

This logs arrays correctly :

console.log(data as any);

This link below is the closest thing I could find, but I am not sure how to apply it to only one index. How to sum elements at the same index in array of arrays into a single array?

Thanks in advance for any help!

I am using Ionic Framework (HTML/CSS files) and Angular (TS files).

Share your data and expected output.

Hassan Imam
– Hassan Imam

2018-01-04 06:24:26 +00:00
Commented Jan 4, 2018 at 6:24 — Hassan Imam
– Hassan Imam, Commented Jan 4, 2018 at 6:24

Sravan · Accepted Answer · 2018-01-04 06:40:52Z

1

Here is a function you can write,

function sum(data, value){
    return data.reduce( function(a, b){
        return a + b[value];
    }, 0);
};

var data = [{ startDate: '', endDate: '', value: 33},
{ startDate: '', endDate: '', value: 97},
{ startDate: '', endDate: '', value: 75}]

alert(sum(data, 'value'))

Please run the above snippet

If you want ts:

function sum(data, value){
    return data.reduce((a, b) => {
        return a + b[value];
    }, 0);
};

edited Jan 4, 2018 at 6:40

answered Jan 4, 2018 at 6:26

Sravan

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