const milestoneData = this.$R.filter(this.$R.propEq('MILESTONE', String(PLANNED_MILESTONE)), this.batchdata)

The code you provided seems to be using the Ramda library in JavaScript. It filters an array called `batchdata` based on a specific condition using `filter()` and `propEq()` functions from Ramda.

Let's break down the code:

const milestoneData = this.$R.filter(
  this.$R.propEq('MILESTONE', String(PLANNED_MILESTONE)),
  this.batchdata
);

Here's what each part does:

1. `this.$R.filter`: Calls the `filter()` function from the Ramda library. It filters an array based on a predicate function.
2. `this.$R.propEq('MILESTONE', String(PLANNED_MILESTONE))`: This is the predicate function used by `filter()`. It checks if the value of the 'MILESTONE' property in each element of `this.batchdata` is equal to the string representation of `PLANNED_MILESTONE`.
3. `this.batchdata`: The array that is being filtered.

The result of this code will be a new array called `milestoneData` that contains only the elements from `this.batchdata` that have a 'MILESTONE' property equal to the string representation of `PLANNED_MILESTONE`.

Please note that the usage of `this.$R` implies that `$R` is an instance of the Ramda library and it is accessible through `this` context.