JavaScript merge array objects with the same keys

Question

I have an array with several objects some have the same keys (Question and QuestionId), for example:

 var jsonData = [ { Question: "Was the training useful?", QuestionId: 1, myData: [{ name: 'No', value: 1 }] }, { Question: "Was the training useful?", QuestionId: 1 , myData: [{ name: 'Yes', value: 1 }] }];

How can I combine these objects into one, expected output:

 var jsonData = [ { Question: "Was the training useful?", QuestionId: 1, myData: [{ name: 'No', value: 1 }, { name: 'Yes', value: 1 }] }];

could initialize a new array, and loop through all your data, looking to see if there's already an instance of your two key value pairs, and if so, add the myData value to the entry in your new array. — async await
– async await, Commented Apr 12, 2022 at 22:09

HellaMad · Accepted Answer · 2022-04-13 02:02:20Z

2

var jsonData = [{ Question: "Was the training useful?", QuestionId: 1, myData: [{ name: 'No', value: 1 }] }, { Question: "Was the training useful?", QuestionId: 1, myData: [{ name: 'Yes', value: 1 }] } ]; const result = Object.values(jsonData.reduce((acc, obj) => { if (!acc[obj.QuestionId]) { acc[obj.QuestionId] = obj; } else { acc[obj.QuestionId].myData = acc[obj.QuestionId].myData ?? []; // if myData is null or undefined, set it to an empty array acc[obj.QuestionId].myData = acc[obj.QuestionId].myData.concat(obj.myData); } return acc; }, {})); console.log(result);

edited Apr 13, 2022 at 2:02

answered Apr 12, 2022 at 22:16

HellaMad

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7 Comments

hncl Over a year ago

That is great thank you. However, it returned two objects, the first is the merged myData, and the second object with the Yes answer, I was hoping to return only one object.

pilchard Over a year ago

@hncl see the snippet, it's working as you expected

HellaMad Over a year ago

@hncl not sure what you mean, can you share the output?

hncl Over a year ago

@HellaMad, it is working now as expected. I have accepted your answer, thanks

hncl Over a year ago

@pilchard, thank you; my challenge is the array is generated using Ajax. I get this error: acc[obj.QuestionId].myData.concat is not a function. I tried to run the script as a function on Ajax complete, still get the same error. Any suggestions?

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Sereyn · Accepted Answer · 2022-04-12 22:33:52Z

function mergeData(data) { const acc = {} data.forEach(x => { const id = x.QuestionId if (!acc[id]) acc[id] = x else acc[id].myData = acc[id].myData.concat(x.myData) }) return Object.values(acc) }

Chris Strickland · Accepted Answer · 2022-04-13 00:07:41Z

You can use forEach to create an object where the keys are the question IDs and then use Object.values to get the values into an array.

var jsonData = [{ Question: "Was the training useful?", QuestionId: 1, myData: [{ name: 'No', value: 1 }] }, { Question: "Was the training useful?", QuestionId: 1 , myData: [{ name: 'Yes', value: 1 }] }]; var temp = {}; jsonData.forEach(x=>{ if(!temp[x.QuestionId]) {temp[x.QuestionId] = x;} else {temp[x.QuestionId].myData.push(x.myData);} }); var arr = Object.values(temp); console.log(arr);

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