Sum values of a specific property in javascript object

Question

On a click event in my application I am returned highlights - an array of features (each time of differing length). So console.log(highlights) produces:

My objective is to return the sum of the values contained in properties.census2010_Pop2010 for each feature in the object. So far I have tried the code below but nothing is returned in the console. Any suggestions would be appreciated.

total = Object.create(null);

highlights.feature.properties.forEach(function (a) {
    a.census2010_Pop2010.forEach(function (b) {
        total = total + b.census2010_Pop2010;
    });
});

console.log(total);

Why do you initialise total as an object? Don't you want it to be a number? — trincot
– trincot, Commented May 10, 2017 at 13:37
You are saying that properties is an array.... it is an object.... You should be doing forEach over the array.... — epascarello
– epascarello, Commented May 10, 2017 at 13:37
It's not clear what you're trying to do here. Your description doesn't match the picture of your source structure. You've said you're trying to sum census2010_Pop2010 "for each feature in the object", but each Feature in the object only has a single properties.census2010_Pop2010 entry, so "summing" doesn't come into it...? — T.J. Crowder
– T.J. Crowder, Commented May 10, 2017 at 13:43

epascarello · Accepted Answer · 2017-05-10 13:44:20Z

11

highlights is an array and you should be looping over that.

var highlights = [
  {properties : { census2010_Pop2010: 10}},
  {properties : { census2010_Pop2010: 20}},
  {properties : { census2010_Pop2010: 30}}
]

var total = highlights.reduce( function(tot, record) {
    return tot + record.properties.census2010_Pop2010;
},0);


console.log(total);

If you want to use forEach it would be like this:

var highlights = [
  {properties : { census2010_Pop2010: 10}},
  {properties : { census2010_Pop2010: 20}},
  {properties : { census2010_Pop2010: 30}}
]

var total = 0;
highlights.forEach( function(record) {
    total += record.properties.census2010_Pop2010;
});


console.log(total);

answered May 10, 2017 at 13:44

epascarello

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Comments

Matt D. Webb · Accepted Answer · 2017-05-10 13:51:49Z

3

This can be achieved by using reduce to total the value of census2010_Pop2010:

const total = highlights.reduce((acc, val) => acc + val.properties.census2010_Pop2010, 0);

Note: I have used the ES6 arrow function to keep it concise, this is not necessary but, becoming more common when adopting a more functional style with methods like map, filter and reduce.

edited May 10, 2017 at 13:51

answered May 10, 2017 at 13:46

Matt D. Webb

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Comments

Chris Rouffer · Accepted Answer · 2017-05-10 18:32:13Z

2

total = 0;

highlights.forEach(function(a) {
    total += Number(a.Feature.properties.census2010_Pop2010);
})
console.log(total);

You need to loop through each of the "Feature" objects in the "highlights" array. You start with a total of 0, then incrementally add the census2010_Pop2010 values from each Feature.

edited May 10, 2017 at 18:32

answered May 10, 2017 at 13:47

Chris Rouffer

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2 Comments

milo526 Over a year ago

Welcome to Stack Overflow! While this code snippet may be the solution, including an explanation really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion.

Chris Rouffer Over a year ago

Thanks milo526. I've updated my answer to include an explanation

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