Javascript nested array: halve items and sum them up

user_12148583 0
Viewed 91

I'm trying to create a function which returns me halve the data sumed up. I was able to do it on a non-nested Array but failing on the nested Array. I get the error Cannot read properties of undefined (reading 'push').

How the returned data should look like:

var data = [{"Key":1,"values":[
{"LastOnline":"21-11-29","Value":2},
{"LastOnline":"21-12-01","Value":2},
{"LastOnline":"21-12-03","Value":2}
]}];

What I have right now:

var data = [{"Key":1,"values":[
{"LastOnline":"21-11-28","Value":1},
{"LastOnline":"21-11-29","Value":1},
{"LastOnline":"21-11-30","Value":1},
{"LastOnline":"21-12-01","Value":1},
{"LastOnline":"21-12-02","Value":1},
{"LastOnline":"21-12-03","Value":1},
]}];

  function halveMonth(data){
    var newData = [];
    var temp = [{"key":data.key,"values":[{}]}];
    // sum 2 togheter
    for(var i=1;i<data.values.length;i++){
      if(data.values[i]){
        temp.values[i].push({"LastOnline":data.values[i].LastOnline, "Value":(data.values[i].Value + data.values[[i-1]].Value)});
      }
    }
    for(var i=0;i<temp.values.length;i++){
      if(i % 2 == 0){
        newData.push(temp.values[i]);
      }
    }
    return newData;
  }
  
  console.log(halveMonth(data));

javascript
5 Answers

The variable data you declare at the first line of your snippet is an array. So you can't do data.values. You first need to indicate which index of your array you want to read. In this case : data[0].values

user_98639520

I would use reduce - saves me from trying to figure out why your two loops do not work other than data.values should be data[0].values

var data = [{"Key":1,"values":[{"LastOnline":"21-11-28","Value":1},{"LastOnline":"21-11-29","Value":1},{"LastOnline":"21-11-30","Value":1},{"LastOnline":"21-12-01","Value":1},{"LastOnline":"21-12-02","Value":1},{"LastOnline":"21-12-03","Value":1},]}];

const newArr = data.slice(0); // to not mutate original
newArr[0].values = data[0].values.reduce((acc,item,i) => { 
  if (i%2 !== 0) { // every second
    acc.push(data[0].values[i]); // push the item
    acc[acc.length-1].Value += data[0].values[i-1].Value; // add the first
  }
  return acc
},[])

console.log(newArr)

user_2957830

First things first, you data is itself an array - so assuming your real data has more than 1 element you'll need to do the same thing for each one.

It's helpful to start off with a method which does the work on just 1 element

const justASingle = {"Key":1,"values":[{"LastOnline":"21-11-28","Value":1},{"LastOnline":"21-11-29","Value":1},{"LastOnline":"21-11-30","Value":1},{"LastOnline":"21-12-01","Value":1},{"LastOnline":"21-12-02","Value":1},{"LastOnline":"21-12-03","Value":1}]};

function halveMonthSingle(data) {

  return {
    ...data,
    values: data.values.reduce((acc, item, idx) => {
      if ((idx % 2) != 0)
        acc.push({
          ...item,
          Value: data.values[idx - 1].Value + item.Value
        })
      return acc;
    }, [])
  }
}

console.log(halveMonthSingle(justASingle))

Once you have that you can just use map do do it for every element

const data = [{"Key":1,"values":[{"LastOnline":"21-11-28","Value":1},{"LastOnline":"21-11-29","Value":1},{"LastOnline":"21-11-30","Value":1},{"LastOnline":"21-12-01","Value":1},{"LastOnline":"21-12-02","Value":1},{"LastOnline":"21-12-03","Value":1}]}];

function halveMonthSingle(data) {

  return {
    ...data,
    values: data.values.reduce((acc, item, idx) => {
      if ((idx % 2) != 0)
        acc.push({
          ...item,
          Value: data.values[idx - 1].Value + item.Value
        })
      return acc;
    }, [])
  }
}

const result = data.map(halveMonthSingle)

console.log(result)

user_2196610

JS variables are case sensitive. Keep the key consistent everywhere. If you don't plan to use reduce here is the solution.

var data = [{"key":1,"values":[
{"LastOnline":"21-11-28","Value":1},
{"LastOnline":"21-11-29","Value":1},
{"LastOnline":"21-11-30","Value":1},
{"LastOnline":"21-12-01","Value":1},
{"LastOnline":"21-12-02","Value":1},
{"LastOnline":"21-12-03","Value":1},
]}];

function halveMonth(data){
let newData = []
for (let i = 0; i < data.length; i++) {
    let temp = {"key":data[i].key,"values":[]}
    for (let j = 0; j < data[i].values.length; j += 2) {
        const res = (j+1===data[i].values.length) ? data[i].values[j].Value : data[i].values[j].Value + data[i].values[j+1].Value
        temp.values.push({"LastOnline":(j+1===data[i].values.length)?data[i].values[j].LastOnline:data[i].values[j+1].LastOnline,"Value":res});
    }
    newData.push(temp);
}
return newData
}
  
  console.log(halveMonth(data));

user_74538570

This works too. I basically did your idea, skipping the temp array and merging the two steps into one.

const data = [{"Key":1,"values":[
    {"LastOnline":"21-11-28","Value":1},
    {"LastOnline":"21-11-29","Value":1},
    {"LastOnline":"21-11-30","Value":1},
    {"LastOnline":"21-12-01","Value":1},
    {"LastOnline":"21-12-02","Value":1},
    {"LastOnline":"21-12-03","Value":1},
    ]}];
    
      function halveMonth(data) {
        const newData = [];
        newData.push({
            Key: data[0].Key,
            values: []
        });

        for(let i = 0; i < data[0].values.length; i++){
            if (i % 2 !== 0) {
                newData[0].values.push({
                    LastOnline: data[0].values[i].LastOnline,
                    Value: data[0].values[i].Value + data[0].values[i-1].Value
                });
            }
        }
        return newData;
      }
      
      console.log(halveMonth(data));

user_159100070
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