Recursive function not returning sum of object values

Question

Why sum is undefined. What am I doing wrong?

var testData1 = [{
  "name": "Doctors",
  "category": "Doctors",
  "subCategory": [{
    "name": "Likes",
    "category": "Likes",
    "subCategory": [{
      "name": "Visit",
      "category": "Visit",
      "subCategory": [{
        "name": "Charges",
        "category": "Charges",
        "subCategory": null,
        "val": 30
      }]
    }]
  }, {
    "name": "Dislikes",
    "category": "Dislikes",
    "subCategory": [{
      "name": "Quality",
      "category": "Quality",
      "subCategory": [{
        "name": "Appointment",
        "category": "Appointment",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Care",
        "category": "Care",
        "subCategory": null,
        "val": 70
      }, {
        "name": "Attentive ",
        "category": "Attentive ",
        "subCategory": null,
        "val": 90
      }]
    }]
  }, {
    "name": "Neutral",
    "category": "Neutral",
    "subCategory": [{
      "name": "Professional ",
      "category": "Professional ",
      "subCategory": [{
        "name": "Ease",
        "category": "Ease",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Competent ",
        "category": "Competent ",
        "subCategory": null,
        "val": 40
      }, {
        "name": "Availability",
        "category": "Availability",
        "subCategory": null,
        "val": 80
      }]
    }]
  }],
  "index": 6
}, {
  "name": "Service",
  "category": "Service",
  "subCategory": [{
    "name": "Likes",
    "category": "Likes",
    "subCategory": [{
      "name": "Environment",
      "category": "Environment",
      "subCategory": [{
        "name": "Professionalism ",
        "category": "Professionalism ",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Room",
        "category": "Room",
        "subCategory": null,
        "val": 30
      }, {
        "name": "Parking",
        "category": "Parking",
        "subCategory": null,
        "val": 20
      }]
    }, {
      "name": "Availability",
      "category": "Availability",
      "subCategory": [{
        "name": "Competent ",
        "category": "Competent ",
        "subCategory": null,
        "val": 30
      }]
    }]
  }, {
    "name": "Dislikes",
    "category": "Dislikes",
    "subCategory": [{
      "name": "Management",
      "category": "Management",
      "subCategory": [{
        "name": "Staff",
        "category": "Staff",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Operations",
        "category": "Operations",
        "subCategory": null,
        "val": 70
      }]
    }, {
      "name": "Nurses",
      "category": "Nurses",
      "subCategory": [{
        "name": "Medicine",
        "category": "Medicine",
        "subCategory": null,
        "val": 30
      }]
    }]
  }, {
    "name": "Neutral",
    "category": "Neutral",
    "subCategory": [{
      "name": "Serving",
      "category": "Serving",
      "subCategory": [{
        "name": "Took long time",
        "category": "Took long time",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Rude",
        "category": "Rude",
        "subCategory": null,
        "val": 40
      }, {
        "name": "Seated",
        "category": "Seated",
        "subCategory": null,
        "val": 80
      }]
    }]
  }],
  "index": 16
}];

function addSum(data) {
  data.forEach(function(d, index) {
    if (Array.isArray(d.subCategory)) {
      return (0 + addSum(d.subCategory));

    } else {

      document.write('<pre>' + JSON.stringify(d.val, 0, 4) + '</pre>');
      return d.val;
    }
  });
}
var sum = addSum(testData1);
alert(sum);

Yeldar Kurmangaliyev · Accepted Answer · 2015-12-30 08:00:42Z

4

Your return does not belong to addSum, it belongs to forEach, and that's why addSum returns nothing (undefined).
Array.prototype.forEach doesn't expect returning values, and cannot be used to calculate sum or something else.

You can utilize Array.prototype.reduce to achieve your result:

function sum(arr)
{
  return arr.reduce(function(a, b) { 
    return Array.isArray(b.subCategory) ? a + sum(b.subCategory) : a + b.val;
  }, 0);
}

sum(testData1);

Or using ECMAScript 6 arrow functions:

var sum = arr => arr.reduce((a, b) => Array.isArray(b.subCategory) 
    ? a + sum(b.subCategory) 
    : a + b.val, 0);

Working JSFiddle demo.

edited Dec 30, 2015 at 8:00

answered Dec 30, 2015 at 7:53

Yeldar Kurmangaliyev

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Comments

Oleksandr T. · Accepted Answer · 2015-12-30 08:36:36Z

2

From .forEach you can't return value, that's why you get undefined, for this case more suitable .reduce method

function addSum(data) {
  return data.reduce(function (p, c) {
    return p + (Array.isArray(c.subCategory) ? addSum(c.subCategory) : c.val);
  }, 0);
}

Example

or if you want use .forEach you can do it like this

function addSum(data) {
  return function sum(data, result) {
    data.forEach(function (element) {
      result = Array.isArray(element.subCategory) 
        ? sum(element.subCategory, result)
        : result + element.val;
    });

    return result;
  }(data, 0);
}

Example

edited Dec 30, 2015 at 8:36

answered Dec 30, 2015 at 7:57

Oleksandr T.

77.6k17 gold badges177 silver badges145 bronze badges

Comments

William Schroeder McKinley · Accepted Answer · 2015-12-30 08:20:26Z

0

You can't return from your foreach, only from your function. Here's a working version of your function:

function addSum(data,tot) {
  tot = tot || 0;
  data.forEach(function(d, index) {
    if (Array.isArray(d.subCategory)) {
      tot = addSum(d.subCategory, tot);
    } else {
      tot += parseInt(d.val);
      document.write('<pre>' + d.val + ' - ' + tot + ' </pre>');
    }
  });
  return tot;
}

and a jsfiddle:

https://jsfiddle.net/mckinleymedia/uk5njxnp/

I agree that this should be simplified to a reduce function, but I thought it would also help to see how to modify what you did to make it work.

answered Dec 30, 2015 at 8:20

William Schroeder McKinley

7686 silver badges15 bronze badges

Comments

HelloWorld · Accepted Answer · 2015-12-30 08:34:59Z

Return in the foreach function is for the callback and does not return from the addSum() function. Foreach callback return will not help in this case. Instead using some external variable for keeping the sum will do the trick.

The updated code below defines a variable sum inside the addSum() function and the return value of recursive call is added to it. The function will now return the calculated sum at the end.

var testData1 = [{
  "name": "Doctors",
  "category": "Doctors",
  "subCategory": [{
    "name": "Likes",
    "category": "Likes",
    "subCategory": [{
      "name": "Visit",
      "category": "Visit",
      "subCategory": [{
        "name": "Charges",
        "category": "Charges",
        "subCategory": null,
        "val": 30
      }]
    }]
  }, {
    "name": "Dislikes",
    "category": "Dislikes",
    "subCategory": [{
      "name": "Quality",
      "category": "Quality",
      "subCategory": [{
        "name": "Appointment",
        "category": "Appointment",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Care",
        "category": "Care",
        "subCategory": null,
        "val": 70
      }, {
        "name": "Attentive ",
        "category": "Attentive ",
        "subCategory": null,
        "val": 90
      }]
    }]
  }, {
    "name": "Neutral",
    "category": "Neutral",
    "subCategory": [{
      "name": "Professional ",
      "category": "Professional ",
      "subCategory": [{
        "name": "Ease",
        "category": "Ease",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Competent ",
        "category": "Competent ",
        "subCategory": null,
        "val": 40
      }, {
        "name": "Availability",
        "category": "Availability",
        "subCategory": null,
        "val": 80
      }]
    }]
  }],
  "index": 6
}, {
  "name": "Service",
  "category": "Service",
  "subCategory": [{
    "name": "Likes",
    "category": "Likes",
    "subCategory": [{
      "name": "Environment",
      "category": "Environment",
      "subCategory": [{
        "name": "Professionalism ",
        "category": "Professionalism ",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Room",
        "category": "Room",
        "subCategory": null,
        "val": 30
      }, {
        "name": "Parking",
        "category": "Parking",
        "subCategory": null,
        "val": 20
      }]
    }, {
      "name": "Availability",
      "category": "Availability",
      "subCategory": [{
        "name": "Competent ",
        "category": "Competent ",
        "subCategory": null,
        "val": 30
      }]
    }]
  }, {
    "name": "Dislikes",
    "category": "Dislikes",
    "subCategory": [{
      "name": "Management",
      "category": "Management",
      "subCategory": [{
        "name": "Staff",
        "category": "Staff",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Operations",
        "category": "Operations",
        "subCategory": null,
        "val": 70
      }]
    }, {
      "name": "Nurses",
      "category": "Nurses",
      "subCategory": [{
        "name": "Medicine",
        "category": "Medicine",
        "subCategory": null,
        "val": 30
      }]
    }]
  }, {
    "name": "Neutral",
    "category": "Neutral",
    "subCategory": [{
      "name": "Serving",
      "category": "Serving",
      "subCategory": [{
        "name": "Took long time",
        "category": "Took long time",
        "subCategory": null,
        "val": 50
      }, {
        "name": "Rude",
        "category": "Rude",
        "subCategory": null,
        "val": 40
      }, {
        "name": "Seated",
        "category": "Seated",
        "subCategory": null,
        "val": 80
      }]
    }]
  }],
  "index": 16
}];

function addSum(data) {
   sum = 0; 
  data.forEach(function(d, index) {
    if (Array.isArray(d.subCategory)) {
      sum += (0 + addSum(d.subCategory));

    } else {

      document.write('<pre>' + JSON.stringify(d.val, 0, 4) + '</pre>');
      sum += d.val;
    }
  });

  return sum;
}
var sum1 = addSum(testData1);
alert(sum1);

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