Arrays

Arrays and lists are fundamental data structures. Here's how different languages handle array creation, manipulation, and iteration.

Array Creation and Initialization

JavaScript

// Array literal
const arr = [1, 2, 3];

// Empty array
const empty = [];

// Array constructor
const arr2 = new Array(1, 2, 3);

// Array with size
const sized = new Array(5);

// Array methods
arr.push(4);        // Add to end
arr.pop();          // Remove from end
arr.unshift(0);     // Add to beginning
arr.shift();        // Remove from beginning

PHP

<?php
// Array literal
$arr = [1, 2, 3];

// Empty array
$empty = [];

// Array function
$arr2 = array(1, 2, 3);

// Associative array
$assoc = ['name' => 'John', 'age' => 30];

// Array methods
array_push($arr, 4);    // Add to end
array_pop($arr);        // Remove from end
array_unshift($arr, 0); // Add to beginning
array_shift($arr);      // Remove from beginning

Rust

// Array (fixed size)
let arr: [i32; 3] = [1, 2, 3];

// Vector (dynamic)
let mut vec = vec![1, 2, 3];

// Empty vector
let mut empty = Vec::new();

// Vector methods
vec.push(4);        // Add to end
vec.pop();          // Remove from end
vec.insert(0, 0);   // Insert at index
vec.remove(0);      // Remove at index

Go

// Slice (dynamic array)
arr := []int{1, 2, 3}

// Empty slice
var empty []int

// Array (fixed size)
var fixed [5]int

// Slice methods
arr = append(arr, 4)  // Add to end
arr = arr[:len(arr)-1] // Remove from end

// Built-in functions
len(arr)              // Length
cap(arr)              // Capacity

Python

# List literal
arr = [1, 2, 3]

# Empty list
empty = []

# List methods
arr.append(4)        # Add to end
arr.pop()            # Remove from end
arr.insert(0, 0)     # Insert at index
arr.remove(2)        # Remove value

# List comprehension
squares = [x**2 for x in range(10)]

Zig

// Array (fixed size)
var arr = [_]i32{ 1, 2, 3 };

// ArrayList (dynamic)
var list = std.ArrayList(i32).init(allocator);
defer list.deinit();

// ArrayList methods
try list.append(4);      // Add to end
_ = list.pop();          // Remove from end
try list.insert(0, 0);   // Insert at index
_ = list.orderedRemove(0); // Remove at index

C#

// Array (fixed size)
int[] arr = {1, 2, 3};

// List (dynamic)
List<int> list = new List<int> {1, 2, 3};

// Empty list
var empty = new List<int>();

// List methods
list.Add(4);           // Add to end
list.RemoveAt(list.Count - 1); // Remove from end
list.Insert(0, 0);     // Insert at index
list.Remove(2);        // Remove value

C++

// Array (fixed size)
int arr[3] = {1, 2, 3};

// Vector (dynamic)
std::vector<int> vec = {1, 2, 3};

// Empty vector
std::vector<int> empty;

// Vector methods
vec.push_back(4);      // Add to end
vec.pop_back();        // Remove from end
vec.insert(vec.begin(), 0); // Insert at beginning
vec.erase(vec.begin());     // Remove at beginning

C

// Array (fixed size)
int arr[3] = {1, 2, 3};

// Empty array
int empty[10];

// No built-in dynamic arrays
// Need to use malloc/realloc for dynamic arrays

// Array access
arr[0] = 10;
int value = arr[1];

Java

// Array (fixed size)
int[] arr = {1, 2, 3};

// ArrayList (dynamic)
ArrayList<Integer> list = new ArrayList<>();
list.add(1);
list.add(2);
list.add(3);

// List methods
list.add(4);           // Add to end
list.remove(list.size() - 1); // Remove from end
list.add(0, 0);        // Insert at index
list.remove(0);        // Remove at index

Ruby

# Array literal
arr = [1, 2, 3]

# Empty array
empty = []

# Array methods
arr << 4              # Add to end (shovel operator)
arr.push(4)           # Add to end
arr.pop               # Remove from end
arr.unshift(0)        # Add to beginning
arr.shift             # Remove from beginning

# Array operations
arr + [4, 5]          # Concatenation
arr * 2               # Repetition

Swift

// Array literal
var arr = [1, 2, 3]

// Empty array
var empty: [Int] = []

// Array methods
arr.append(4)         // Add to end
arr.removeLast()      // Remove from end
arr.insert(0, at: 0)   // Insert at index
arr.remove(at: 0)      // Remove at index

// Array operations
arr + [4, 5]          // Concatenation

Array Manipulation

JavaScript

const arr = [1, 2, 3, 4, 5];

// Map
const doubled = arr.map(x => x * 2);

// Filter
const evens = arr.filter(x => x % 2 === 0);

// Reduce
const sum = arr.reduce((acc, x) => acc + x, 0);

// Find
const found = arr.find(x => x > 3);

// Slice
const slice = arr.slice(1, 3);  // [2, 3]

// Sort
const sorted = [...arr].sort((a, b) => b - a);

PHP

<?php
$arr = [1, 2, 3, 4, 5];

// Map
$doubled = array_map(fn($x) => $x * 2, $arr);

// Filter
$evens = array_filter($arr, fn($x) => $x % 2 === 0);

// Reduce
$sum = array_reduce($arr, fn($acc, $x) => $acc + $x, 0);

// Find
$found = array_search(4, $arr);

// Slice
$slice = array_slice($arr, 1, 2);  // [2, 3]

// Sort
$sorted = $arr;
rsort($sorted);

Rust

let arr = vec![1, 2, 3, 4, 5];

// Map
let doubled: Vec<i32> = arr.iter().map(|x| x * 2).collect();

// Filter
let evens: Vec<i32> = arr.iter().filter(|x| x % 2 == 0).collect();

// Reduce (fold)
let sum: i32 = arr.iter().fold(0, |acc, x| acc + x);

// Find
let found = arr.iter().find(|x| **x > 3);

// Slice
let slice = &arr[1..3];  // [2, 3]

// Sort
let mut sorted = arr.clone();
sorted.sort_by(|a, b| b.cmp(a));

Go

arr := []int{1, 2, 3, 4, 5}

// Map (manual)
doubled := make([]int, len(arr))
for i, v := range arr {
  doubled[i] = v * 2
}

// Filter (manual)
var evens []int
for _, v := range arr {
  if v%2 == 0 {
      evens = append(evens, v)
  }
}

// Sort
import "sort"
sorted := make([]int, len(arr))
copy(sorted, arr)
sort.Ints(sorted)

Python

arr = [1, 2, 3, 4, 5]

# Map
doubled = list(map(lambda x: x * 2, arr))
# Or list comprehension
doubled = [x * 2 for x in arr]

# Filter
evens = list(filter(lambda x: x % 2 == 0, arr))
# Or list comprehension
evens = [x for x in arr if x % 2 == 0]

# Reduce
from functools import reduce
sum_val = reduce(lambda acc, x: acc + x, arr, 0)

# Find
found = next((x for x in arr if x > 3), None)

# Slice
slice = arr[1:3]  # [2, 3]

# Sort
sorted_arr = sorted(arr, reverse=True)

Zig

var arr = [_]i32{ 1, 2, 3, 4, 5 };

// Manual operations
var doubled: [5]i32 = undefined;
for (arr, 0..) |val, i| {
  doubled[i] = val * 2;
}

// Filter (manual)
var evens = std.ArrayList(i32).init(allocator);
for (arr) |val| {
  if (val % 2 == 0) {
      try evens.append(val);
  }
}

// Sort
std.mem.sort(i32, &arr, {}, comptime std.sort.asc(i32));

C#

var arr = new[] {1, 2, 3, 4, 5};

// Map
var doubled = arr.Select(x => x * 2).ToArray();

// Filter
var evens = arr.Where(x => x % 2 == 0).ToArray();

// Reduce (Aggregate)
var sum = arr.Aggregate(0, (acc, x) => acc + x);

// Find
var found = arr.FirstOrDefault(x => x > 3);

// Slice
var slice = arr[1..3];  // C# 8+

// Sort
var sorted = arr.OrderByDescending(x => x).ToArray();

C++

std::vector<int> vec = {1, 2, 3, 4, 5};

// Transform (map)
std::vector<int> doubled;
std::transform(vec.begin(), vec.end(), 
             std::back_inserter(doubled),
             [](int x) { return x * 2; });

// Remove if (filter)
vec.erase(std::remove_if(vec.begin(), vec.end(),
                       [](int x) { return x % 2 != 0; }),
        vec.end());

// Accumulate (reduce)
int sum = std::accumulate(vec.begin(), vec.end(), 0);

// Find
auto found = std::find_if(vec.begin(), vec.end(),
                        [](int x) { return x > 3; });

// Sort
std::sort(vec.begin(), vec.end(), std::greater<int>());

C

int arr[] = {1, 2, 3, 4, 5};
int size = 5;

// Manual operations
int doubled[5];
for (int i = 0; i < size; i++) {
  doubled[i] = arr[i] * 2;
}

// Filter (manual)
int evens[5];
int count = 0;
for (int i = 0; i < size; i++) {
  if (arr[i] % 2 == 0) {
      evens[count++] = arr[i];
  }
}

// Sort (qsort)
#include <stdlib.h>
int compare(const void* a, const void* b) {
  return *(int*)b - *(int*)a;
}
qsort(arr, size, sizeof(int), compare);

Java

List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);

// Map
List<Integer> doubled = list.stream()
  .map(x -> x * 2)
  .collect(Collectors.toList());

// Filter
List<Integer> evens = list.stream()
  .filter(x -> x % 2 == 0)
  .collect(Collectors.toList());

// Reduce
int sum = list.stream()
  .reduce(0, (acc, x) -> acc + x);

// Find
Optional<Integer> found = list.stream()
  .filter(x -> x > 3)
  .findFirst();

// Sort
List<Integer> sorted = list.stream()
  .sorted(Collections.reverseOrder())
  .collect(Collectors.toList());

Ruby

arr = [1, 2, 3, 4, 5]

# Map
doubled = arr.map { |x| x * 2 }

# Filter
evens = arr.select { |x| x.even? }

# Reduce
sum = arr.reduce(0) { |acc, x| acc + x }

# Find
found = arr.find { |x| x > 3 }

# Slice
slice = arr[1, 2]  # [2, 3]

# Sort
sorted = arr.sort.reverse

Swift

let arr = [1, 2, 3, 4, 5]

// Map
let doubled = arr.map { $0 * 2 }

// Filter
let evens = arr.filter { $0 % 2 == 0 }

// Reduce
let sum = arr.reduce(0) { $0 + $1 }

// Find
let found = arr.first { $0 > 3 }

// Slice
let slice = Array(arr[1..<3])  // [2, 3]

// Sort
let sorted = arr.sorted(by: >)

Key Takeaways

• Fixed vs dynamic -- C, Zig, and Go use fixed-size arrays (e.g., int arr[3] in C, var arr = [_]i32{1,2,3} in Zig). JavaScript, Python, Ruby, and PHP use dynamic lists by default. Rust offers both: [T; N] for fixed size and Vec<T> for dynamic. Choose fixed arrays when size is known at compile time and you want stack allocation; use dynamic structures when the size varies at runtime or you need frequent resizing.

• Slices -- Go slices ([]int) are the primary dynamic type and reference underlying arrays. Rust and Zig use slice references (&[T]) for zero-copy views. Python and C# use slice syntax (arr[1:3], arr[1..3]) for subarrays. Slices avoid copying data—essential for performance when passing subranges. Prefer languages with slice support when building parsers, stream processors, or APIs that frequently pass array segments.

• Map, filter, reduce -- JavaScript, Python, Ruby, and Swift provide built-in map, filter, and reduce methods. C# uses LINQ (Select, Where, Aggregate). Java uses Streams. Go and C require manual loops. Choose languages with first-class functional primitives when doing data transformation pipelines; otherwise, expect more verbose imperative code.

• Add/remove operations -- Most languages use push/pop for end operations (e.g., arr.push(4) in JavaScript, vec.push(4) in Rust). Go uses append(arr, 4) and slicing for removal. Zig's ArrayList requires explicit allocation and try list.append(4). Consider API ergonomics: if you need frequent insertions at arbitrary positions, Python's list.insert() or Ruby's arr.unshift may be simpler than C's manual reallocation.

• Functional style vs manual loops -- Languages like JavaScript and Python let you chain arr.map(x => x*2).filter(x => x > 0). Go and C force explicit loops. Java Streams bridge the gap with .map().filter().collect(). If your team prefers declarative code, favor JavaScript, Python, or Java; for maximum control and minimal abstraction, C or Go works better.