CODEWITHSUNDEEP
functional-programmingramda.js
brickleberry
brickleberry

Reputation: 522

Please how do i achieve the following using ramda

I have a random array of numbers 1 to five occurring in ramdom sometimes [1,1,1,1,2,2] etc. I am tasked with finding the value with highest occurrence all the the time regardless. I achieved that in javascript like below using a library called ramda here . After reading the documentation, i went with a solution like below.

// filter out duplication in array that way you can get the uniq represented numbers
const uniqueItems = R.uniq(params);

// use the unique numbers as keys and create a new array of object
 const mappedItemsWithRepresentations = map((a) => ({ color: a, rep: params.filter(b => b === a).length }), uniqueItems);

// and then finally, select the item with highest rep and return it key
const maxRepItem = mappedItemsWithRepresentations.reduce((acc, curr) => acc.rep > curr.rep ? acc : curr, []);

return maxRepItem.key; // gives me the correct value i need

However, reading through more in the documentation and going through the example here, i realised there is a way i can combine the logic above and simply with ramda. I tried numerous attempt possible and the closest i could get are below.

const getMaxRep = curry(pipe(uniq, map((a) => ({ color: a, rep: filter(b => b === a).length })), pipe(max(pathEq("rep")), tap(console.log))));

console.log("Max Rep here", getMaxRep(params));

I also tried utilising the reduced feature here, all to no avail. Please how do i arrange achieve that ? Any help will be appreciated.

Upvotes: 1

Views: 356

Answers (3)

Yasser Nascimento
Yasser Nascimento

Reputation: 1381

nice use case, try this:

const maxReduce = reduce(maxBy(last), [0,0])
const getMaxRep = pipe(countBy(identity), toPairs, maxReduce, head)

console.log(getMaxRep([1,1,1,1,2,2]))

countBy is a really nice start, sadly Ramda don't support reduce for object but we can convert to an array of arrays using toPairs function and finish the work.

Upvotes: 2

Ori Drori
Ori Drori

Reputation: 193047

Ramda has R.countBy to get the number of occurrences. You can convert the resulting object of country to pairs [value, count], and then reduce it to find the pair with the highest count:

const { pipe, countBy, identity, toPairs, reduce, maxBy, last, head } = R

const fn = pipe(
  countBy(identity), // count the occurrences 
  toPairs, // convert to pairs of [value, count]
  reduce(maxBy(last), [0, 0]), // reduce to find the maximum occurrence
  head, // get the actual value
  Number, // convert back to an number
)

const arr = [1,1,1,1,2,2]

const result = fn(arr)

console.log(result)
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script>

A slight variation on this idea that collects values with the same count to an array. This will handle cases in which the frequency of several items is identical:

const { pipe, countBy, identity, toPairs, invert, reduce, maxBy, last, head, map } = R

const fn = pipe(
  countBy(identity), // count the occurrences 
  invert, // combine all values with the same count
  toPairs, // convert to pairs of [value, count]
  reduce(maxBy(head), [0, 0]), // reduce to find the maximum occurrence
  last, // get the actual values
  map(Number), // convert back to numbers
)

const arr = [1,1,1,1,2,2,3,3,3,3]

const result = fn(arr)

console.log(result)
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script>

Upvotes: 2

Scott Sauyet
Scott Sauyet

Reputation: 50807

It's not entirely clear to me what it is you're asking for.

But it might be something like this:

const maxRep = pipe (
  countBy (identity),
  toPairs,
  map (zipObj(['color', 'rep'])), 
  reduce (maxBy (prop ('rep')), {rep: -Infinity}),
)

const params = [1, 2, 3, 4, 2, 3, 5, 2, 3, 2, 1, 1, 4, 5, 5, 3, 2, 5, 1, 5, 2]

console .log (
  maxRep (params)
)
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.27.0/ramda.js"></script>
<script> const {pipe, countBy, identity, toPairs, map, zipObj, reduce, maxBy, prop} = R </script>

We start with a list of values drawn from {1, 2, 3, 4, 5}, occuring in some random, multiply-occuring order.

With countBy(identity) we change the original list into something like 

{"1": 4, "2": 6, "3": 4, "4": 2, "5": 5}

with the counts associated with each entry.

toPairs formats that as an array like 

[["1", 4], ["2", 6], ["3", 4], ["4", 2], ["5", 5]]

(You could also use Object.entries here.)

Then by calling map (zipObj (['color', 'rep'])), we turn this into

[{"color": "1", "rep": 4}, {"color": "2", "rep": 6}, ...]

Finally, we reduce the result, using maxBy (prop ('rep')), which chooses the one with the maximum rep value. For the initial value to the max call, we create a dummy object, {rep: -Infinity} that will compare less than any in your list.

If you wanted to also keep that final intermediate structure, you could rename that function to makeReps, dropping off the last function in the pipeline, and then making a new maxRep out of it.

Then you could call

const reps = makeResps (params)
const maxVal = maxRep (reps)

and use both.

But all this presupposes that the value with color and rep properties is what you need. If you just need the count then the other solutions already here handle that fine.

Upvotes: 1

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