What standard functions for working with collections in Kotlin do you know?

Standard functions for working with collections in Kotlin are very diverse and allow performing many operations:

Transformation operations:

• map: Transforms each element of the collection into a new element, returning a new collection with the results.
• flatMap: Transforms each element into a collection of elements and combines all resulting collections into one.
• zip: Creates pairs from elements of two collections with the same indices.
• unzip: Splits a collection of pairs into two collections.

Filtering operations:

• filter: Returns a collection containing only elements that satisfy the given predicate.
• filterNotNull: Returns a new collection containing only non-null elements.
• filterIsInstance: Returns a collection containing only elements of the specified type.
• distinct: Returns a collection with unique elements.
• drop: Returns a collection without the first N elements.
• dropLast: Returns a collection without the last N elements.
• take: Returns the first N elements of the collection.
• takeLast: Returns the last N elements of the collection.

Ordering operations:

• sorted: Returns a sorted collection in natural order.
• sortedBy: Returns a collection sorted by the result of a specified selector for each element.
• sortedDescending: Returns a collection sorted in reverse natural order.
• sortedByDescending: Returns a collection sorted in reverse order by the result of a specified selector.
• reversed: Returns a list with elements in reverse order.

Aggregation (reduction) operations:

• fold: Reduces the collection to a single value by applying a function to an accumulator and each element, with an initial accumulator value.
• reduce: Reduces the collection to a single value by applying a function to an accumulator and each element, starting with the first element as the initial accumulator.
• sum: Calculates the sum of all numeric elements in the collection.
• average: Calculates the average of numeric elements in the collection.
• count: Returns the number of elements in the collection.
• maxOrNull: Returns the maximum element or null if the collection is empty.
• minOrNull: Returns the minimum element or null if the collection is empty.
• maxByOrNull: Returns the element for which the specified selector returns the maximum value.
• minByOrNull: Returns the element for which the specified selector returns the minimum value.

Element search operations:

• find: Returns the first element satisfying the predicate or null.
• findLast: Returns the last element satisfying the predicate or null.
• first: Returns the first element.
• last: Returns the last element.
• firstOrNull: Returns the first element or null if the collection is empty.
• lastOrNull: Returns the last element or null if the collection is empty.
• indexOf: Returns the index of the first occurrence of the specified element.
• lastIndexOf: Returns the index of the last occurrence of the specified element.
• single: Returns the single element if present; throws an exception if there are no elements or more than one.
• singleOrNull: Returns the single element or null if there are no elements or more than one.

Operations on parts of the collection:

• slice: Returns a list of elements at specified indices.
• chunked: Divides the collection into lists of a specified size.
• windowed: Creates sliding windows of a specified size.

Grouping operations:

• groupBy: Groups elements by a key, returning a Map where the key is the result of the selector function, and the value is a list of elements with that key.
• groupingBy: Returns a Grouping object that allows lazy aggregations over groups.

Check operations:

• all: Checks if all elements satisfy the predicate.
• any: Checks if any element satisfies the predicate.
• none: Checks if no elements satisfy the predicate.
• contains: Checks if the collection contains the specified element.
• isEmpty: Checks if the collection is empty.
• isNotEmpty: Checks if the collection is not empty.

This is just a part of the standard functions available for working with collections in Kotlin. Many of them have overloads for different collection types and parameters.

Example of using map:

// List of numbers
val numbers = listOf(1, 2, 3, 4, 5)

// Transform each number into its square
val squares = numbers.map { it * it }

// squares: [1, 4, 9, 16, 25]

Example of using filter:

// List of strings
val fruits = listOf("apple", "banana", "cherry", "date")

// Filter by string length greater than 5
val longFruits = fruits.filter { it.length > 5 }

// longFruits: [banana, cherry]