CODEWITHSUNDEEP
javascriptarrays
Marcel Dz
Marcel Dz

Reputation: 2714

Count values inside a specific array length

I'm searching for a nice approach for the following task: I have a game with rounds. In each round we have a number between 1-10.

This is how I'm doing it so far but I'm stuck.

gameValues.forEach(function(x) { counts[x] = (counts[x] || 0)+1; });

I want to count the double entrees in my array but I only want to watch out for the last 5 rounds.

Round 6 ( We already have 5 values ):
gameValues = [9,9,9,2,1]
result: 9:3, 2:1, 1:1,

Round 7 ( Now we have 6 values but I only want to count the first 5):
gameValues = [3,9,9,9,2,1]
result: 3:1, 9:3, 2:1,

I can't manage to only count the last 5 rounds..

Upvotes: 1

Views: 74

Answers (4)

DecPK
DecPK

Reputation: 25398

You can get the last 5 numbers in an array using splice and then using reduce you can get the counts of each number.

The splice() method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place. To access part of an array without modifying it, see slice().

function countLastFive(arr) {
  return arr.splice(-5).reduce((acc, curr) => {
    acc[curr] = acc[curr] ? ++acc[curr] : 1;
    return acc;
  }, {});
}

console.log(countLastFive([9, 9, 9, 2, 1, 3, 1]));
console.log(countLastFive([9, 9, 9, 2, 1]));
console.log(countLastFive([3, 9, 9, 9, 2, 6, 4, 3, 2, 1]));

Just be sure that the slice changes the original array. So it would be better to clone the array so that It won't change the original array

function countLastFive(arr) {
  return arr.splice(-5).reduce((acc, curr) => {
    acc[curr] = acc[curr] ? ++acc[curr] : 1;
    return acc;
  }, {});
}

const arr1 = [9, 9, 1, 9, 2, 1];
const arr2 = [9, 9, 1, 9, 2, 1];

console.log("Before -> arr1 => ", arr1);
console.log(countLastFive(arr1));
console.log("After -> arr1 => ", arr1);

console.log("Before -> arr2 => ", arr2);
console.log(countLastFive([...arr2]));
console.log("After -> arr2 => ", arr2);

Upvotes: 2

Tom el Safadi
Tom el Safadi

Reputation: 6746

const gameValues = [3,9,9,9,2,1]
    
const uniq = gameValues.splice(-5)
  .map((number) => {
    return {
      count: 1,
      number: number
  }})
  .reduce((a, b) => {
    a[b.number] = (a[b.number] || 0) + b.count
    return a
  }, {})
 
console.log(uniq);

Upvotes: 2

astroide
astroide

Reputation: 817

Use gameValues.slice(-5) to get the last 5 values of the array, then do the same count operation :


gameValues = [3,9,9,9,2,1]
counts = {}
gameValues.slice(-5).forEach(function(x) { counts[x] = (counts[x] || 0)+1; });
console.log(counts);
// { '1': 1, '2': 1, '9': 3 }

Upvotes: 3

PaulS
PaulS

Reputation: 940

You might want to slice the array before looping through it.

gameValues.slice(-5).forEach(function(x) { counts[x] = (counts[x] || 0)+1; });

Upvotes: 2

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