implement aggregate transformer

[100pah]

At present the there is only a simplest aggregate transformer in echarts-simple-transform/aggregate. We should better implement a built-in aggregate transformer in echarts.

About the API

Think of whether the API of echarts-simple-transform/aggregate appropriate.

About group by

In echarts-simple-transform/aggregate only on dimension can be set in group by. Do we need to support multiple dimension group by?

About Methods

Some methods of aggregate already roughly implemented in echarts-simple-transform/aggregate:

• sum
• count
• first
• average
• Q1
• Q2/median
• Q3
• min
• max

We need to make sure they are implemented correctly.

Other methods we may implement:

• distinct: The count of distinct dimension values.
• variance: The sample variance of dimension values.
• variancep: The population variance of dimension values.
• stdev: The sample standard deviation of dimension values.
• stdevp: The population standard deviation of dimension values.
• stderr: The standard error of dimension values.
• product: The product of dimension values.
• valid: The count of dimension values that are not null, undefined, '', NaN, '-', or determined by user defined validation function.
• ... anything else useful?

Some references: vega aggregate.

About math calculation precision

We all known that the floating precision issue (like 0.1 + 0.2). It might bring trouble in some scenarios like:

• The math result is needed to be displayed in label.
• The sum should equal to 100%.
• Multiple by 100, 1000, ...

Some cases:

0.1 + 0.2 === 0.30000000000000004
2.3 - 0.3 === 1.9999999999999998
33643.2 - 15918.3 === 17724.899999999998
146.39 - 62.83 === 83.55999999999999
1.09 - 0.13 === 0.9600000000000001
0.1 * 0.2 === 0.020000000000000004
16.08 * 100 === 1607.9999999999998
146.39 * 100 === 14638.999999999998
9999999999999999 === 10000000000000000
-11.699999999999986 === -11.699999999999987

We should also take care the toFixed bug like:

1.005.toFixed(2) === '1.00' // rather than '1.01'
0.1.toFixed(20) === '0.10000000000000000555'

Solution:

• A. Do not care about it until some users required.
• B. Try to resolve it:
  • For arithmetic: use addSafe we already have and implement multipleSafe in appropriate place.
  • For comparison of two numbers, use:

  const EPSILON = (function () { // Solve compatibility issues
      return Number.EPSILON ? Number.EPSILON : Math.pow(2, -52);
  })();
  function compare(a, b){
      return Math.abs(a - b) < EPSILON;
  }

See: IEEE 754, http://0.30000000000000004.com/, camsong/blog#9, https://javascript.info/number#imprecise-calculations, ... (lots of related references)

Some library:

• https://github.com/nefe/number-precision
• mathjs

  (math.add(math.bignumber(0.1),math.bignumber(0.2)))

• decimal.js

  x = new Decimal(0.1)
  y = 0.2
  console.log(x.plus(y).toString()

• bignumber.js
• big.js

About big number

Do not support.

Test

Could find some test cases in some other math libraries.

[maneetgoyal]

Would be great to have this feature 💯

[sumitnegi7]

@100pah Seems like a pretty useful feature

[saikat-samanta]

This feature seems really helpful. 👍

[Prit-sangani]

Yes, this feature is very helpful. Would be great to have this feature.

[VirajBhatt9]

It is a very great feature. It would be very helpful to have this feature.