CODEWITHSUNDEEP
javascriptfunctional-programmingcurryingpointfreeramda.js
Chad
Chad

Reputation: 2071

How to convert simple average function in javascript to pointfree form using Ramda?

How do I convert the following simple average function to pointfree form (using Ramda)?

var _average = function(xs) {
  return R.reduce(R.add, 0, xs) / xs.length;
};

I've been this for a while now, but the R.divide function is throwing me off since the numerator and the denominator requires evaluation first

Upvotes: 3

Views: 1003

Answers (4)

Nagibaba
Nagibaba

Reputation: 5348

Simpler one:

R.mean([1,3]) // returns 2

Upvotes: 0

davidchambers
davidchambers

Reputation: 24806

Using R.converge:

//    average :: Array Number -> Number
const average = R.converge(R.divide, [R.sum, R.length]);

Using R.lift (which a more generally applicable function than R.converge):

//    average :: Array Number -> Number
const average = R.lift(R.divide)(R.sum, R.length);

Upvotes: 8

Karpak
Karpak

Reputation: 1927

You can try the below one

var _sum = function(xs) {
  return R.reduce(R.add, 0, xs);
};

var _average = function(xs) {
  return R.divide(_sum(xs), xs.length);
};

console.log(_average([3,4,5,6]));

or simply

var _average = function(xs) {
  return R.divide(R.reduce(R.add, 0, xs), xs.length);
};

console.log(_average([3,4,5,6]));

Upvotes: 0

MinusFour
MinusFour

Reputation: 14423

Here's one way to do it:

let xs = [5, 5];
let average = R.compose(R.apply(R.divide), R.juxt([R.sum, R.length]));
console.log(average(xs));
<script src="//cdn.jsdelivr.net/ramda/latest/ramda.min.js"></script>

Basically, R.juxt maps the array values into R.sum and R.length which gives you an array with the sum of the array and the length of the array. The result is applied to R.divide.

Upvotes: 5

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