Kotlin filter map by value. Each key has a … Maps in Kotlin 1.

Kotlin filter map by value. This method allows you to create a subset of the original map based on specific value conditions. In cases A collection that holds pairs of objects (keys and values) and supports retrieving the value corresponding to each key, checking if a collection holds a particular key or a value. They’re the Swiss Army knife in your coding toolkit. entries (which gives you each key with its corresponding value) rather than myStringMap. 0 Return the destination map. Kotlin provides several ways to filter collections easily and efficiently using its functional programming paradigms. mapNotNull { it. Map keys are unique; the Jul 4, 2025 · When transforming maps, you have two options: transform keys leaving values unchanged and vice versa. Jan 1, 2025 · Note that both methods create a new map with the added key-value pair because the map in Kotlin is immutable. To transform the type of the value, you need to map the values from Any? to Any, by doing a cast. Mar 19, 2024 · Not all of these functions can be used on Maps, however, all filter functions that work on Maps will work on Arrays. A list is a generic ordered collection of elements. 0 Samples xxxxxxxxxx val originalMap = mapOf("key1" to 1, "key2" to 2, "something_else" to 3) val filteredMap = originalMap. Jan 24, 2024 · Create, initialize, add item, get value, update, remove entries in a Kotlin HashMap - Iterate over a HashMap - Filter, transform a HashMap example Apr 12, 2023 · Maps are an essential data structure in Kotlin programming, used for storing key-value pairs, where each key is unique. These key-value pairs are known as entries of a map. Kotlin Map and mapOf Method: A Complete Guide Introduction Kotlin's Map and mapOf methods are integral parts of the Kotlin programming language. Builds a new read-only Map by populating a MutableMap using the given builderAction and returning a read-only map with the same key-value pairs. collections package and come with a variety of implementations tailored to Dec 10, 2024 · Conclusion Mastering Kotlin Flow operators is essential for Android developers aiming to build responsive, efficient, and scalable applications. g. By understanding how to use lambda functions and combining filters with other collection operations, you can write concise and efficient Kotlin code. The standard library contains a group of extension functions that let you filter collections in a single call. associateBy({it. These functions provide the tools required to write clean, concise, and useful transformations on data. Jun 21, 2022 · In this article, we will learn how to transform a list using a map function in Kotlin, and how to filter the list with whichever criteria we like. We will be using lambda functions, which provide a great way to do functional programming. We will go through the syntax of filter () extension function and some examples. Dec 5, 2024 · In Kotlin, maps are collections of key-value pairs and are part of the Map interface, which extends the Collection interface. Let's explore how to use these functions with examples. The resulting SortedMap determines the equality and order of keys according to the sorting order provided by the given comparator. To filter a map based on values in Kotlin, you can use the `filterValues` method to create a new map containing only the key-value pairs that meet the filter criteria. filterValues{ someCondition }. This implementation makes no guarantees regarding the order of enumeration of keys, values and entries collections. 0 Samples Apr 11, 2025 · Grouping Edit page 11 April 2025 The Kotlin standard library provides extension functions for grouping collection elements. In contrast, the same value can be associated with several unique keys. Jun 10, 2019 · I have HashMap in Kotlin val map = HashMap<String, String>() I want to know how to get key for a particular value from this HashMap without iterating through complete HashMap? Nov 30, 2024 · Maps in Kotlin are a powerful and flexible way to handle key-value pairs. 1 Samples Mar 18, 2018 · How to collect to Map from List where null values are excluded/skipped? May 30, 2023 · Basics of the Kotlin filter() operator As developers, we transform, manipulate, and filter data on a regular basis; to make this task easier, we can use Kotlin collection operations. Key-based access to map entries enables various map-specific processing capabilities from getting a value by key to separate filtering of keys and values. In your case, this solution will work. These collections are part of Kotlin’s standard library and provide various functionalities to store, retrieve, and manipulate data efficiently. That said, neither Java stream nor Kotlin's filter will help here, since those return new collections and don't affect the original one. Nullability is an integral part of Kotlin's type system, and understanding how to navigate it can lead to more robust and error-resistant code. Further, we’ll also see how each approach handles the scenario of conflicting elements, where the default behavior is to give preference to elements Jan 29, 2024 · This article shows how to filter list values in Kotlin language. Kotlin Map filter () Returns a new map containing all key-value pairs matching the given predicate. In this map, each key is the lambda result, and the corresponding value is the List of elements on which this result is returned. Unlike lists or sets, maps allow you to associate a unique key with a specific value, making them invaluable for tasks like indexing, grouping, and quick lookups. Whether you are fetching and transforming API data, handling user inputs, or Jun 15, 2025 · The Kotlin Standard Library provides useful functions like groupBy () and groupingBy () to easily perform grouping operations on collections. Mar 19, 2024 · 2. In this blog post… Mar 19, 2024 · A Map maintains key-value associations. The requirement is that, if you want to create a changing Map, you must use the changeable map type. When working with data or collection elements in Kotlin, you have to use either the Set, Map, or filter() operator to manipulate data. And mapNotNull will take only non null values and put them in the list (which is finally returned). These expressions return true when the provided element matches the predicate and false when it doesn’t match. Samples xxxxxxxxxx val originalMap = mapOf("key1" to 1, "key2" to 2, "key3" to 3) val destinationMap = mutableMapOf("key40" to 40, "key50" to 50) Dec 22, 2019 · I'm replacing my current implementation using RxJava to Coroutines and Flow. Apr 7, 2025 · In this article, we’ve explored various ways to skip null values when converting a list of pairs to a map in Kotlin. By merging two maps, we can combine the key-value pairs from the two maps into a single one. if = is not present in the string. This method allows you to sort the map based on values. Maps are part of the Kotlin Standard Library and are also known as dictionaries or associative arrays in other programming languages. The primary characteristic of a map is its ability to map keys to values, which means each key is associated with exactly one value. Nov 1, 2015 · I have a map where the values are strings and the keys are lists: Map<String, List<BoMLine>> materials I'd like to filter this map by its values; something like this: materials. Oct 14, 2020 · Although the Kotlin Standard Library contains a filterValues function that seems to be appropriate, this function does not do any type conversions, resulting in a Map which won’t contain null values, but is still a Map with values of a nullable type according to the compiler. For instance, we may need to filter certain key-value pairs based on a particular condition, or we may need to modify certain values in the maps. Kotlin Map s Maps are a common data structure in computer science. I'm trying to filter the list of items inside a Flow before providin Kotlin sequences are lazily evaluated, like Java streams. So your best et is to use val filtered: Map<String, Any Sep 10, 2024 · Maps in Kotlin are a collection of key-value pairs, and Kotlin map filter allows you to refine these pairs based on a predicate. Note that this collection may contain duplicate values. The same value can be associated with multiple Sep 11, 2023 · In Kotlin, filtering conditions are defined by predicates – lambda functions that take a collection element and return a boolean value: true means that the given element matches the predicate, false means the opposite. The elements in the resulting list are in the same order as they were in the source array. Consider the following example to grasp its fundamentals: fun main() { val numbers = listOf(1, 2 Jul 3, 2024 · The mapOfNotNull function in Kotlin is used to create a map while filtering out any null values. Kotlin provides two main functions to create maps: mapOf and mutableMapOf. They allow developers to efficiently store and retrieve data in key-value pairs. Basically your current onQueryTextChange implementation creates Apr 12, 2018 · } Copy Output -- Example 2. Stateful operations require a significant amount of state Mar 19, 2024 · Take a closer look at Kotlin's get operator and explore different approaches to get a not-null value from a Map. With both immutable and mutable options, Kotlin maps cater to various use cases—from a static map for reading to a dynamic one for manipulation during runtime. A collection that holds pairs of objects (keys and values) and supports retrieving the value corresponding to each key, as well as adding new, removing or updating existing pairs. We look at some of the options and which is more efficient at runtime. println shortcut Java Bubble Converts this Map to a SortedMap. Introduction Maps are a key collection type in programming, designed to store key-value pairs. out. By understanding how to use operators like map, filter, combine, and flatMapLatest, you can manipulate data streams effectively to create seamless user experiences. Apr 26, 2022 · However, Kotlin enables users to create changeable maps, or maps that can be changed after they’ve been created. In Kotlin, we can easily create maps using the mapOf () method. Oct 29, 2024 · Kotlin maps are a versatile and powerful tool for managing key-value pairs. Let's delve into Kotlin maps, how they work, and the differences between immutable and mutable maps. In Kotlin, maps are part of the kotlin. In case if any two entries are mapped to the equal keys, the value of the latter one will overwrite the value associated with the former one. startsWith("bbb") }. 0 Samples Learn how to use the `filter` function on Map instances in Kotlin with detailed explanations and code examples. The transformation logic is encapsulated as a lambda expression, and the return value forms the new elements of the resulting list. For maps, known to have no null keys, you needlessly pay the null comparison for every entry. Jul 22, 2019 · Basically, check if there's only a single value in the list, if so, then return the value. A predicate Aug 23, 2024 · Like map() and forEach(), filter() takes a single lambda expression as a parameter. myPairStr. On this page, we provide descriptions of the map processing functions from the standard library. Introduction A map is a collection of key-value pairs. Working with Kotlin maps is a common occurrence. In a map, keys are unique, two keys can’t be the same. I'm having some trouble using some Flow operators. filterkeys { it. They’re also known as dictionaries or associative arrays in other programming languages. Returns a list containing only distinct elements from the given array. Each key in a map is unique, and it can only be associated with one value. For example - under Manufacturer we have got values "brand" or "producer") b) The parameter value (e. 1. We use predicates to define the filtering conditions. Using it outside of the function produces an unspecified behavior. Kotlin makes filtering easy and powerful using functions like filter (), filterNot (), filterIndexed (), and partition (). Dec 5, 2024 · Filtering lists in Kotlin is a common task when you want to isolate elements that satisfy certain conditions. You have to use predicates to define the filtering collection when using the Dec 5, 2024 · Understanding how to use lambdas with map, filter, and reduce functions in Kotlin can greatly enhance your ability to work with collections more effectively. productName},{it. In this tutorial, we’ll discuss the different scenarios of this problem and explore how to find the maximum entry in a Nov 19, 2024 · Kotlin, a modern and expressive language, offers robust support for collections, including lists, sets, and maps. That doesn't apply to Kotlin lists, so in that case you'd first apply filter on all items, then map all the items passing the filtering step, and finally you'd only take the first item out of the resulting list. Further, EnumFinder defines the from () function to get the corresponding instance from valueMap. Complex operations are built upon this functionality and provided in form of kotlin. Returns a new Map with entries having the keys obtained by applying the transform function to each entry in this Map and the values of this map. Sep 1, 2024 · How to Use Maps in Kotlin A map is a collection of key-value pairs. In the example above, I have used both for Loop and filter function to get my desired result. 0 Samples Jan 17, 2025 · The sequence operations can be classified into the following groups regarding their state requirements: Stateless operations require no state and process each element independently, for example, map() or filter(). Dec 5, 2024 · In Kotlin, a map is a collection of key-value pairs, where each key is unique and maps to exactly one value. Kotlin filter list example In the first example, we use the filter Dec 5, 2024 · Maps in Kotlin are a powerful data structure that allow you to store key-value pairs, providing efficient data retrieval by the use of keys. Maps also allow iterating over keys, values or key-value pairs (entries). From creating and accessing maps to performing advanced operations, understanding maps is crucial for any Kotlin developer. val map = prices. To sort a map by values in Kotlin, you can convert the map entries to a list, sort the list by values, and then convert it back to a map. New to Kotlin wanted to know if there was a different way, maybe using map. Dec 5, 2024 · Handling null values when working with maps and key-value lookups in Kotlin is an important skill for any developer. values It returns a read-only Collection of all values in this map. Table of Contents Introduction mapOfNotNull Function Syntax Understanding mapOfNotNull Examples Basic Usage Combining Nullable and Non Dec 5, 2024 · Maps are key-value pairs and are integral for storing and efficiently accessing dynamic data within applications. These filtering functions are based on something called a predicate. Returns a read-only Collection of all values in this map. To use the Map interface in Kotlin, you need to use its function, called mapOf() or mapOf<k,v>(). This function allows you to initialize a map with key-value pairs where null values are excluded, ensuring that the resulting map contains only non-null entries. That’s why Sequences achieve 18 steps instead of 23 as Iterables did. Jan 29, 2024 · Kotlin map tutorial shows how to work with maps in Kotlin. Dec 5, 2024 · In Kotlin, handling maps and sorting them either by keys or values can indeed be a common requirement. split("="). Map keys are unique; the map holds only one value for each key. The compiler can't know that the predicate you pass to filter () makes sure all the values of the filtered map are non-null, so it can't use type inference. Feb 11, 2021 · Map-specific operations Edit page 11 February 2021 In maps, types of both keys and values are user-defined. filterKeys { it. Both functions use the transformations that take a map entry as an argument, so you can operate both its key and value. 1 Inheritors Dec 5, 2024 · Understanding Maps in Kotlin A map is an Kotlin interface that holds key-value pairs, much like dictionaries in Python or hash tables in Java. You want to group nozzle states by shift ID, create user ID and nozzle ID. Whether you’re building Android maps with Kotlin or handling complex data structures on the server side Jun 1, 2022 · Where: a) String (key) is the value of the filter key (The key in the filter map has the main value and any other names under it. collections extension functions. However, when working with maps, we’re often presented with situations that require us to transform them in some way. DataFrame object is Returns a map containing all key-value pairs with keys matching the given predicate. Apr 21, 2025 · Maps in Kotlin transform how developers handle key-value data. These functions allow you to create read-only and mutable maps, respectively. In other Dec 21, 2018 · So to get all the values from a map, you can just use the built-in values property on the map like this. Among equal elements of the given array, only the first one will be present in the resulting list. In your initial solution - that without covariance on K -, the Returns a new map with entries having the keys of this map and the values obtained by applying the transform function to each entry in this Map. 2 -- key : A, value : 10 key : B, value : 20 key : C, value : 30 key : D, value : 40 Copy References Kotlin Map Kotlin filterKeys Kotlin forEach kotlin filter, for loop, foreach, kotlin, map Intellij IDEA – System. size >= 2 } } The takeIf function will return null if the size of the list returned by split method is 1 i. Since Kotlin 1. Note that if the comparator considers any two keys of this map equal, only the value associated with the last of them gets into the resulting map. Returns a map containing all key-value pairs with values matching the given predicate. The filter method returns a list containing only elements matching the given predicate. 1 -- A = 10 -- Example 2. filter Oct 24, 2025 · Edit page Last modified: 24 October 2025 Data transformation pipeline usually consists of several modification operations, such as filtering, sorting, grouping, pivoting, adding/removing columns etc. If I understand correctly, you thus want a different group for each distinct combination of shift ID, create user ID and nozzle ID. This comprehensive guide will cover the Map interface, the mapOf method, their syntax, usage, and practical examples. In this article, we'll explore different ways you can filter lists with conditions in Kotlin. 2. e. So you need to create a class representing such a combination (let's name if Key), and group the elements by their Key Jul 31, 2023 · Then using map. May 3, 2019 · You can use mapNotNull instead of map. Feb 28, 2024 · Map is a popular data structure commonly used in most Kotlin applications. However, truly harnessing the power of these functional programming style methods takes some practice. Nike) is assigned to the ParameterValue object (val value: String). second }[0] Groups values returned by the valueTransform function applied to each element of the original array by the key returned by the given keySelector function applied to the element and returns a map where each group key is associated with a list of corresponding values. toList(). Each key has a … Maps in Kotlin 1. The returned map preserves the entry iteration order of the keys produced from the original array. 1 -- A = 10 B = 20 C = 30 D = 40 -- Example 2. Nov 11, 2016 · How to use `filter` on Map instance in Kotlin? Asked 8 years, 11 months ago Modified 8 years, 11 months ago Viewed 13k times Dec 27, 2023 · As an Android developer leveraging Kotlin daily, map () and filter () have become indispensable weapons in my arsenal for working with collections and transforming data. 0 Samples Sep 7, 2024 · There are a few ways to iterate over the keys and values in a Kotlin map. To apply a given transformation to keys, use mapKeys(); in turn, mapValues() transforms values. The Kotlin collections documentation gives us information on whether we can use a filter function on only arrays or both. Jun 13, 2022 · May be worth adding that if OP wants to use the key in setting the corresponding value (which I suspect was the intent), then probably better to start from myStringMap. They provide efficient storage and constant-time lookups, which make them a popular choice for various tasks where data needs to be accessed Mar 5, 2018 · I am probably missing something very obvious: How do I efficiently filter and iterate through the entries of a HashMap in Kotlin? I want to do the following: myMap. takeIf { it. In this article, we will look into how to perform these tasks efficiently using Kotlin's powerful collection processing functions. The map passed as a receiver to the builderAction is valid only inside that function. By the end, you'll have a clear understanding of how Jun 3, 2019 · リストや配列のフィルタ (filter, filterNot) コレクションの要素から、指定した条件を満たす要素のみを抽出するには、 filter 関数を使用します。次の例では、数値リストから偶数のみを抽出しています。 Dec 6, 2021 · You should generally avoid using Java streams in Kotlin, there are a ton of functions on collections in the stdlib that make stream+op+collect redundant (you can just use the operation directly). get (foundKey) to get the String Value. But this freedom comes with a cost. First, we discussed the programmatic approach involving iterating a list and removing any null or empty elements. . The filterNotNull () method filters out null values from the list, while the mapNotNull () method applies a transformation on each element of the list and returns a new list containing only non-null transformed values. Mar 19, 2024 · 1. The predicates are simple lambda expressions. 0 Samples Returns a list containing only elements matching the given predicate. In this tutorial, we’ll explore multiple ways to merge two maps in Kotlin. These functions help us handle and transform lists into meaningful maps based on certain conditions. Understanding how to effectively use maps will significantly enhance your ability to manage collections of data in Kotlin. This task is a common operation and presents an exciting challenge. f Jan 18, 2024 · Let's explore the use of maps in the Kotlin language and discuss the difference between HashMap and MutableMap in Kotlin. In this chapter, we'll learn all about them, including mutable and immutable maps, map operations like forEach() and filter(), and how to convert lists into maps with associate() and groupBy(). This article explores `map`, `filter`, and `reduce` in Kotlin, their syntax, use cases, and practical examples. productPrice}) val values = map. Working with maps in Kotlin is a common task, especially when dealing with structured or paired data. Dec 5, 2024 · Maps in Kotlin are a versatile collection type that pair unique keys to corresponding values. If you want to modify the existing map, you need to use mutable maps. Ever found yourself struggling with structured data relationships? Kotlin’s map collections provide an elegant solution with impressive performance characteristics. contains("key") } println 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. What have I prepared: fun filterParameters( Feb 18, 2017 · The filter functions return a Map with the same generic types as the original map. Kotlin has powerful methods for filtering list data. A predicate is a single-argument method that returns a boolean value. Sep 16, 2023 · Kotlin’s Flow is a powerful asynchronous programming construct that allows you to work with sequences of values emitted over time. Mar 19, 2024 · This map holds the V->E relations, which are value -> enum instance relations. With filterKeys and filterValues, you can specifically target either the keys or values of the map. asSequence(). These functions return a new List and are usable for both read-only and mutable Lists. Nov 11, 2019 · A word of warning, concerning the covariance out K? Yes, it offers the possibility to use the same method not only for Map<String?, Stuff?> but also for Map<String, Stuff?> (key nullable or not). Feb 27, 2024 · Kotlin - get unique list values for only certain filter from list Asked 1 year, 5 months ago Modified 1 year, 5 months ago Viewed 591 times More Related Answers kotlin empty map printing a map in kotlin kotlin empty map hashmap kotlin kotlin filter list kotlin map foreach list map by index and value Oct 31, 2017 · Get entry with max value from Map in Kotlin Asked 7 years, 10 months ago Modified 5 years, 7 months ago Viewed 25k times Apr 16, 2019 · I have an array: var month: List<String> = arrayListOf("January", "February", "March") I have to filter the list so I am left with only "January". In maps, types of both keys and values are user-defined. 0 Samples Oct 24, 2025 · filter Edit page Last modified: 24 October 2025 Returns DataFrame with rows that satisfy row condition Related operations: Filter rows Properties Strings Apr 7, 2025 · This article explored ways to remove null and empty values from a List in Kotlin. Mar 7, 2019 · Let's say the class of the elements of your collection is NozzleState. 0 Samples Maps in Kotlin are used to associate keys and values. The lambda has a single parameter representing each item in the collection and returns a Boolean value. But is it possible to avoid the for loop and filter and map both the Collections in single line of code? Sep 5, 2024 · The Kotlin list filter function is a powerful tool for filtering collections based on given predicates. May 10, 2025 · In Kotlin, working with collections like lists, sets, and maps is very common. The Kotlin DataFrame API is designed in functional style so that the whole processing pipeline can be represented as a single statement with a sequential chain of operations. Dec 5, 2024 · Understanding map in Kotlin The map function in Kotlin is used to transform each element of a collection by applying a given function to it, resulting in a new list. To… Sep 5, 2024 · Kotlin map is a collection of key-value pairs or entries. This method allows you to create a subset of the original map based on specific key conditions. Nov 21, 2023 · After all, there is no need to filter and map elements when we already have our first 4 elements. In the case that there isn't (you get null), then you can map the value. Sometimes, we want to find the maximum entry from a Kotlin Map. Jul 7, 2025 · Explore how to use map, filter, reduce, zip, groupBy, and other advanced collection functions in Kotlin for functional-style data transformation. map{ it. The returned map preserves the entry iteration order of the original map. The basic function groupBy() takes a lambda function and returns a Map. filter option, Thanks! -Thanks for your response! Took pieces of code and currently have map. Maps can store a collection of zero or more key-value pairs. In this article, we will explore how to add, update, and remove entries in a map in Kotlin. Stateless operations can also require a small constant amount of state to process an element, for example, take() or drop(). Mar 19, 2024 · The standard Kotlin library provides many beneficial functions to filter a List. values. One of the most useful tasks is filtering, that means selecting only the elements that meet a certain condition. Aug 12, 2018 · val date: String ) Provided the given code above, I am trying to return a list of Expenses that match with the dates from another list of Strings. entrySe Appends all entries matching the given predicate into the mutable map given as destination parameter. This article will help you dive into iterating these maps using powerful iteration patterns available in Kotlin, specifically focusing on the `for` loop. Hash table based implementation of the MutableMap interface. bvpz t8b uw7 b1tvg nj udq gtv bcp rd5r4l bwo

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