How to Filter a Map Based on Keys in Kotlin

How to Filter a Map Based on Keys in Kotlin ?

Answer

To filter a map based on keys in Kotlin, you can use the `filterKeys` method to create a new map containing only the key-value pairs that meet the filter criteria. This method allows you to create a subset of the original map based on specific key conditions.

✐ Examples

1 Filtering a Map Based on Key Range

We can filter a map based on a range of keys in Kotlin by using the `filterKeys` method to create a new map containing only the key-value pairs that fall within the specified range.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the filterKeys method to filter the map based on the specified key range.
We print the filtered map to the console using the println function to verify the filtering.

Kotlin Program

fun main() {
    // Declare and initialize a map
    val myMap = mapOf(1 to "one", 2 to "two", 3 to "three", 4 to "four", 5 to "five")

    // Define the key range
    val lowerBound = 2
    val upperBound = 4

    // Filter the map based on the key range
    val filteredMap = myMap.filterKeys { it in lowerBound..upperBound }

    // Print the filtered map
    println("Filtered Map by Key Range: $filteredMap")
}

Output

Filtered Map by Key Range: {2=two, 3=three, 4=four}

2 Filtering a Map Based on Specific Keys

We can filter a map based on specific keys in Kotlin by using the `filterKeys` method to create a new map containing only the key-value pairs that match the specified keys.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We define a set of specific keys that we want to filter the map by.
We use the filterKeys method to filter the map based on the specified keys.
We print the filtered map to the console using the println function to verify the filtering.

Kotlin Program

fun main() {
    // Declare and initialize a map
    val myMap = mapOf(1 to "one", 2 to "two", 3 to "three", 4 to "four", 5 to "five")

    // Define the specific keys to filter by
    val keysToFilter = setOf(1, 3, 5)

    // Filter the map based on the specific keys
    val filteredMap = myMap.filterKeys { it in keysToFilter }

    // Print the filtered map
    println("Filtered Map by Specific Keys: $filteredMap")
}

Output

Filtered Map by Specific Keys: {1=one, 3=three, 5=five}

3 Filtering a Map with String Keys Based on Prefix

We can filter a map with string keys based on a specific prefix in Kotlin by using the `filterKeys` method to create a new map containing only the key-value pairs that have keys starting with the given prefix.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and string values.
We define a prefix string that we want to filter the map by.
We use the filterKeys method to filter the map based on the specified prefix.
We print the filtered map to the console using the println function to verify the filtering.

Kotlin Program

fun main() {
    // Declare and initialize a map
    val myMap = mapOf("apple" to "fruit", "banana" to "fruit", "carrot" to "vegetable", "apricot" to "fruit", "blueberry" to "fruit")

    // Define the prefix to filter by
    val prefix = "ap"

    // Filter the map based on the prefix
    val filteredMap = myMap.filterKeys { it.startsWith(prefix) }

    // Print the filtered map
    println("Filtered Map by Prefix: $filteredMap")
}

Output

Filtered Map by Prefix: {apple=fruit, apricot=fruit}

Summary

In this tutorial, we learned How to Filter a Map Based on Keys in Kotlin language with well detailed examples.

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