How to loop through a javascript object and sum amounts in a new object

Question

I have a javascript object

const data = {
  type: "FeatureCollection",
  features: [{
    type: "Feature",
    geometry: {
      type: "Point",
      coordinates: [-118.4158548, 33.9811315]
    },
    properties: {
      name: "John Smith",
      total_due: 1
    }
  }, {
    type: "Feature",
    geometry: {
      type: "Point",
      coordinates: [-122.4605458, 37.7286008]
    },
    properties: {
      name: "June Waters",
      total_due: 50
    }
  }, {
    type: "Feature",
    geometry: {
      type: "Point",
      coordinates: [-122.4120835, 37.7778926]
    },
    properties: {
      name: "John Smith",
      total_due: 2
    }
  }, {
    type: "Feature",
    geometry: {
      type: "Point",
      coordinates: [-118.3508279, 34.0701918]
    },
    properties: {
      name: "June Waters",
      total_due: 60
    }
  }, {
    type: "Feature",
    geometry: {
      type: "Point",
      coordinates: [-82.4000143, 34.8518747]
    },
    properties: {
      name: "Mike Jones",
      total_due: 30
    }
  }]
};

What I'd like to do is loop through the object, add the unique names to a new object and sum the totals. The new object would look like this:

newObject = {'June Waters':110, 'Mike Jones':30, 'John Smith': 3}

I tried to do the following but I'm so new to JS so I don't know what I'm doing.

var newObject = {}
  
data.features.forEach(function (item) {
  newObject.item.properties.name = newObject.item.properties.name + item.properties.total_due
});

The following is a portion of the error that is generated.

TypeError: Cannot read properties of undefined (reading 'properties')
    at c:\Users\ryanj\z\const data =.js:10:18
    at Array.forEach (<anonymous>)....

Any help or hints would be truly appreciated.

cmgchess · Accepted Answer · 2022-02-25 18:56:36Z

you ran into an error because newObject.item is undefined since empty object therefore any property you are trying to access beyond that such as properties is not found

by doing some tweaks to your implementation. I'm adding the name to the newObject if it already doesn't exist then i proceed to add the totals

const data = {"type": "FeatureCollection","features": [{"type": "Feature","geometry": {"type": "Point","coordinates": [-118.4158548, 33.9811315]},"properties": {"name": "John Smith","total_due": 1}},{"type": "Feature","geometry": {"type": "Point","coordinates": [-122.4605458, 37.7286008]},"properties": {"name": "June Waters","total_due": 50}},{"type":"Feature","geometry": {"type": "Point","coordinates": [-122.4120835, 37.7778926]},"properties": {"name": "John Smith","total_due": 2}},{"type": "Feature","geometry": {"type": "Point","coordinates": [-118.3508279, 34.0701918]},"properties": {"name": "June Waters","total_due": 60}},{"type": "Feature","geometry": {"type": "Point","coordinates": [-82.4000143, 34.8518747]},"properties": {"name": "Mike Jones","total_due": 30}}]};

var newObject = {}
  
data.features.forEach(function (item) {
    if(!newObject[item.properties.name])newObject[item.properties.name] = 0;
  newObject[item.properties.name] = newObject[item.properties.name] + item.properties.total_due
});

console.log(newObject)

similarly you can use reduce for these type of problems

const data = {"type": "FeatureCollection","features": [{"type": "Feature","geometry": {"type": "Point","coordinates": [-118.4158548, 33.9811315]},"properties": {"name": "John Smith","total_due": 1}},{"type": "Feature","geometry": {"type": "Point","coordinates": [-122.4605458, 37.7286008]},"properties": {"name": "June Waters","total_due": 50}},{"type":"Feature","geometry": {"type": "Point","coordinates": [-122.4120835, 37.7778926]},"properties": {"name": "John Smith","total_due": 2}},{"type": "Feature","geometry": {"type": "Point","coordinates": [-118.3508279, 34.0701918]},"properties": {"name": "June Waters","total_due": 60}},{"type": "Feature","geometry": {"type": "Point","coordinates": [-82.4000143, 34.8518747]},"properties": {"name": "Mike Jones","total_due": 30}}]};

let total = data.features.reduce((acc,curr) =>{
    if(!acc[curr.properties.name])acc[curr.properties.name]=0;
  acc[curr.properties.name]+=curr.properties.total_due;
  return acc;
},{})

console.log(total)

ElyasAsmad · Accepted Answer · 2022-02-25 19:00:34Z

In Javascript, you can refer to an object properties using the square brackets [] just like what we do in an array.

In this code, firstly we check whether the key is already defined in the object. If it is not defined, we will simply assign the value of total_due to the key (which in this case is the name of the person). In the next iteration, if Javascript recognises the key and the value of the key is not undefined, we simply add the total_due value to the current key value.

let finalData = {}
data.features.forEach((item) => {
    if (finalData[item.properties.name] === undefined) {
        finalData[item.properties.name] = item.properties.total_due;
    }
    else {
        finalData[item.properties.name] += item.properties.total_due;
    }
})

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