使用对象键作为日期以获取平均值

Question

I have an object like so. They key is a timestamp and the value is my number

var history = {
     '1505845390000': 295426,
     '1505757979000': 4115911,
     '1505677767000': 4033384,
     '1505675472000': 4033384,
     '1505591090000': 3943956,
     '1505502071000': 3848963,
     '1505499910000': 3848963,
     '1505499894000': 3848963
}

What I want to do is:

1) For the latest 5 dates (keys), get an average of the values 2) For a date range, get an average of the values

Answer 1

you can do the following for the first case

 var obj = { '1505845390000': 295426, '1505757979000': 4115911, '1505677767000': 4033384, '1505675472000': 4033384, '1505591090000': 3943956, '1505502071000': 3848963, '1505499910000': 3848963, '1505499894000': 3848963 } let ans = Object.keys(obj).sort(); ans = ans.slice(ans.length-5).reduce((a, b) => a+obj[b], 0); console.log(ans/5); 

For the 2nd case you can do

 var obj = { '1505845390000': 295426, '1505757979000': 4115911, '1505677767000': 4033384, '1505675472000': 4033384, '1505591090000': 3943956, '1505502071000': 3848963, '1505499910000': 3848963, '1505499894000': 3848963 } let start = '1505591090000', end = '1505845390000' let ans = Object.keys(obj).filter(e => e>=start && e<=end); let result = ans.reduce((a,b) => a+obj[b],0)/ans.length console.log(result); 

Answer 2

This answer has a good explanation of how to filter an object by its keys:

https://stackoverflow.com/a/38750895/5009210

Basically use Object.keys() to get an array of keys, then Array.filter() to select the ones you want, then Array.reduce() to reconstruct an object with the relevant values for the filtered keys. Like this:

Object.keys( history )
   .filter( someFilterFunction )
   .reduce( (obj, key) => {
      obj[key] = history[key];
   }, {});

Once you've done this, you can extract the remaining values using Object.values() and then pass them to a simple average function (I assume you want the mean average):

function meanAverage( valuesToAverage ) {
    //avoid divide by zero
    if ( valuesToAverage.length ) {
       const valueSum = sum( valuesToAverage );
       return valueSum / valuesToAverage.length;
    }
    return 0;
}

function sum( valuesToSum ) {
   return valuesToSum.reduce( (a, b) => a + b );
}