JavaScript - Reduce Array of Objects by Key [duplicate]

问题

Working with an array of objects like:

const arr = [
  {name: "qewregf dqewafs", value: "qewregf dqewafs answer", count: 2},
  {name: "survey with select", value: "survey with select answer", count: 2},
  {name: "werasd", value: "Donald", count: 1},
  {name: "werasd", value: "Jim", count: 1}
];

I am trying to reduce the array on matching values for the name key and achieve an desired output like:

desiredOutput = [
  {name: "qewregf dqewafs", data: [{value: "qewregf dqewafs answer", count: 2}]},
  {name: "survey with select", data: [{value: "survey with select answer", count: 2}]},
  {name: "werasd", data: [{value: "Donald", count: 1}, {value: "Jim", count: 1}]}
]

This attempt reduces the array, but I am missing how to merge the nested values without overwriting.

const arr = [{"name":"qewregf dqewafs","value":"qewregf dqewafs answer","count":2},{"name":"survey with select","value":"survey with select answer","count":2},{"name":"werasd","value":"Donald","count":1},{"name":"werasd","value":"Jim","count":1}];

const result = arr.reduce((acc, d) => {
  const found = acc.find(a => a.name === d.name);
  const value = { name: d.name, val: d.value };
  if (found) {
    acc.push(...value);
  }
  else {
    acc.push({ name: d.name, data: [{ value: d.value }, { count: d.count }] });
  }
  return acc;
}, []);

console.log(result);

What am I missing?

回答1:

You codes are a little close to the goal, just need to adjust something.

Please see the comment in below demo:

When acc.find doesn't find anything, then push one element {name:d.name, data: [value]}
if found, then push one {value: ...} into data property.

const arr = [
  {name: "qewregf dqewafs", value: "qewregf dqewafs answer", count: 2},
  {name: "survey with select", value: "survey with select answer", count: 2},
  {name: "werasd", value: "Donald", count: 1},
  {name: "werasd", value: "Jim", count: 1}
];

const result = arr.reduce((acc, d) => {
  const found = acc.find(a => a.name === d.name);
  //const value = { name: d.name, val: d.value };
  const value = { value: d.value, count: d.count }; // the element in data property
  if (!found) {
    //acc.push(...value);
    acc.push({name:d.name, data: [value]}) // not found, so need to add data property
  }
  else {
    //acc.push({ name: d.name, data: [{ value: d.value }, { count: d.count }] });
    found.data.push(value) // if found, that means data property exists, so just push new element to found.data.
  }
  return acc;
}, []);

console.log(result)

回答2:

You could simplify the use of the found object by checking if it does not exist and push a new object to the result set.

Then push an object with value and count to data.

const
    array = [{ name: "qewregf dqewafs", value: "qewregf dqewafs answer", count: 2 }, { name: "survey with select", value: "survey with select answer", count: 2 }, { name: "werasd", value: "Donald", count: 1 }, { name: "werasd", value: "Jim", count: 1 }],
    result = array.reduce((r, { name, value, count }) => {
        var temp = r.find(o => name === o.name);
        if (!temp) {
            r.push(temp = { name, data: [] });
        }
        temp.data.push({ value, count });
        return r;
    }, []);

console.log(result);

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回答3:

You need to do something like this:

const arr = [
  {name: "qewregf dqewafs", value: "qewregf dqewafs answer", count: 2},
  {name: "survey with select", value: "survey with select answer", count: 2},
  {name: "werasd", value: "Donald", count: 1},
  {name: "werasd", value: "Jim", count: 1}
];

const result = arr.reduce((acc, d) => {
  let idx = acc.findIndex(a => a.name === d.name);
  let val = { value: d.value, count: d.count };

  if (idx > -1) {
    acc[idx].data.push(val);
  } else {
    acc.push({ name: d.name, data: [val] });
  }

  return acc;
}, []);

console.log(result);

You have to find the index first, and then push your data into that row. You're just finding it but then pushing a new value to the array.

回答4:

You're not far off. This would be a simple change to two lines of your code to achieve it:

const arr = [
  {name: "qewregf dqewafs", value: "qewregf dqewafs answer", count: 2},
  {name: "survey with select", value: "survey with select answer", count: 2},
  {name: "werasd", value: "Donald", count: 1},
  {name: "werasd", value: "Jim", count: 1}
];

const result = arr.reduce((acc, d) => {
  const found = acc.find(a => a.name === d.name);
  const value = { name: d.name, val: d.value };
  if (found) {
    found.data.push(value);
  }
  else {
    acc.push({ name: d.name, data: [{ value: d.value, count: d.count }] });
  }
  return acc;
}, []);

console.log(result)

Here are the differences:

-     acc.push(...value);
+     found.data.push(value);


-    acc.push({ name: d.name, data: [{ value: d.value }, { count: d.count }] });
+    acc.push({ name: d.name, data: [{ value: d.value, count: d.count }] });

回答5:

Simply create a map with name as key and use Object destructing and Object.values() to get the desired result.

const arr = [
  {name: "qewregf dqewafs", value: "qewregf dqewafs answer", count: 2},
  {name: "survey with select", value: "survey with select answer", count: 2},
  {name: "werasd", value: "Donald", count: 1},
  {name: "werasd", value: "Jim", count: 1}
];

let result = Object.values(arr.reduce((a,{name, ...props})=>{
  if(!a[name])
     a[name]  = Object.assign({}, {name,data : [props]});
   else
    a[name].data.push(props);
  return a;
},{}));

console.log(result);

来源：https://stackoverflow.com/questions/51935559/javascript-reduce-array-of-objects-by-key

标签

javascript

arrays

javascript-objects