如何使用reduce（）（ES6）计算总数？

Question

I have data which has season and fielding array. fielding array has 3 parameters Catches , Runouts , Stumpings . I want to calculate total Catches , Stumpings , Runouts .

var data = [
    {
    season:2015,
    fielding:{Catches:2, Runouts:1, Stumpings:1
    },
    {
    season:2016,
    fielding:{Catches:0, Runouts:1, Stumpings:1
    },
    {
    season:2016,
    fielding:{Catches:0, Runouts:0, Stumpings:0
    },
    {
    season:2017,
    fielding:{Catches:1, Runouts:3, Stumpings:1
    },
    {
    season:2017,
    fielding:{Catches:2, Runouts:1, Stumpings:2
    }
]

I want final output as object as follows:

Catches -> 2+0+0+1+2 = 5
Runouts -> 1+1+0+3+1 = 6
Stumpings -> 1+1+0+1+2 =5

What I tried :

let dismissals = data.reduce( (a,{season, fielding})  => {

            if(!a[fielding.Catches]){
                a[fielding.Catches] = {};
            }else if(a[fielding.Runouts]){
                a[fielding.Runouts] = {};
            }else if(a[fielding.Stumpings]){
                a[fielding.Stumpings] = {};
            }else{
                a[fielding.Stumpings] += 1;
                a[fielding.Runouts] += 1;
                a[fielding.Catches] += 1;
            }

            return a;
        }, {});

My code does not calculate required output and gives NaN .

Answer 1

Iterate over the entries of fielding , and add the value to the [key] in the accumulator (defaulting to 0 if the key doesn't exist yet):

 var data=[{season:2015,fielding:{Catches:2,Runouts:1,Stumpings:1}},{season:2016,fielding:{Catches:0,Runouts:1,Stumpings:1}},{season:2016,fielding:{Catches:0,Runouts:0,Stumpings:0}},{season:2017,fielding:{Catches:1,Runouts:3,Stumpings:1}},{season:2017,fielding:{Catches:2,Runouts:1,Stumpings:2}}]; console.log( data.reduce((a, { fielding }) => { Object.entries(fielding).forEach(([key, val]) => { if (key !== '_id') a[key] = (a[key] || 0) + val; }); return a; }, {}) ); 

Answer 2

You could use reduce and loop fielding 's Object.keys

 const res = data.reduce((a, {fielding}) => Object.keys(fielding).forEach(f => a[f] = (a[f] || 0) + fielding[f]) || a , Object.create(null)); console.log(res); 

 <script> var data = [ { season:2015, fielding:{Catches:2, Runouts:1, Stumpings:1} }, { season:2016, fielding:{Catches:0, Runouts:1, Stumpings:1} }, { season:2016, fielding:{Catches:0, Runouts:0, Stumpings:0} }, { season:2017, fielding:{Catches:1, Runouts:3, Stumpings:1} }, { season:2017, fielding:{Catches:2, Runouts:1, Stumpings:2} } ]; </script>