Daily Challenge #172 - Find All in an Array

Setup

Implement a function that will accept an array of integers and an integer n. Find all occurrences of n in the given array and return another array containing all the index positions of n in the array.

If n is not in the given array, return an empty array [].

Assume thatn and all values in the array will always be integers.

Example

find_all([6, 9, 3, 4, 3, 82, 11], 3)
> [2, 4]

Tests

[6, 9, 3, 4, 3, 82, 11], 3
[10, 16, 20, 6, 14, 11, 20, 2, 17, 16, 14], 16
[20, 20, 10, 13, 15, 2, 7, 2, 20, 3, 18, 2, 3, 2, 16, 10, 9, 9, 7, 5, 15, 5], 20

---

This challenge comes from MementoMori on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

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Comments

[Valts Liepiņš]

Ruby

def findAll xs, x
    xs.filter_map.with_index {|y, i| i if x == y}
end

[Mitesh Kamat]

In JavaScript:
function find_all1(arr, n){
let arr1 = [];
arr.forEach((item,index) => {
item === n ? arr1.push(index): null;
});
console.log(arr1);
}

find_all1([6,9,3,4,3,82,11],3);

[Jesse Phillips]

// D
pure nothrow @safe
auto findIndex(const(int)[] arr, size_t needle) {
  return arr.enumerate
     .filter!(x => x[1] == needle) 
     .map!(x => x[0])
     //.array
     ;
} unittest {
  assert(findIndex([6, 9, 3, 4, 3, 82, 11], 3).equal([2, 4]));
} 

The commented out array line would allocate a new array to meet the specification.

[Ryan Beckett]

Swift:

func findOccurances(of numberToFind: Int, in listOfNumbers: [Int]) -> [Int] {
    return listOfNumbers.enumerated().compactMap { (index, number) in
        number == numberToFind ? index : nil
    }
}

[Amin]

Elm

import List exposing (indexedMap, filter, map)
import Tuple exposing (pair, second, first)


findAll : List Int -> Int -> List Int
findAll integers integer =
    indexedMap pair integers
        |> filter (second >> (==) integer)
        |> map first

Implementation.

[Ciaran Treanor]

Rust:

fn find_all(numbers: Vec<usize>, value: usize) -> Vec<usize> {
    numbers.iter()
        .enumerate()
        .filter(|&(_, val)| *val == value)
        .map(|(index, _)| index)
        .collect()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test1() {
        assert_eq!(vec![2, 4], find_all(vec![6, 9, 3, 4, 3, 82, 1], 3));
        assert_eq!(vec![1,9], find_all(vec![10, 16, 20, 6, 14, 11, 20, 2, 17, 16, 14], 16));
        assert_eq!(vec![0,1,8], find_all(vec![20, 20, 10, 13, 15, 2, 7, 2, 20, 3, 18, 2, 3, 2, 16, 10, 9, 9, 7, 5, 15, 5], 20));
    }
}

[Ebrahim Hasan]

PHP


<?php function find_all($array,$number){
return array_keys($array,$number);

}
var_dump(find_all(array(6, 9, 3, 4, 3, 82, 11), 3) );


[Craig McIlwrath]

Haskell:

import Data.List (findIndices) 

findAll :: Eq a => a -> [a] -> [Int]
findAll x = findIndices (==x) 

or alternatively,

findAll :: Eq a => a -> [a] -> [Int]
findAll x = map fst . filter ((==x) . snd) . zip [0..]

[Nguyễn Trọng Vĩnh]

const findAll = (array, n) => array.reduce((prev, next, index) => next === n ? [...prev, index] : prev, []);

[SavagePixie]

JavaScript

const findAll = (arr, n) => arr
   .reduce((a, b, i) => b === n
      ? a.concat(i)
      : a
   , [])