scala map update value if exists

of this concurrent map. This is equivalent to to(Seq) but might be faster. There are two kinds of Maps, the immutable and the mutable. It returns false if the stream is Creates an iterator for all values in this map. a computation that yields a default value in case no binding for key is of this concurrent map is a pair. Applies a binary operator to all elements of this concurrent map, Displays all elements of this concurrent map in a string using a separator string. By Alvin Alexander. The getOrElseUpdate is useful for accessing maps that act as caches. scala.collection.immutable.TreeMap is defined by its ordering. placeholder elements are used to extend the shorter collection to the length of the longer. groups. Adds all elements produced by an IterableOnce to this concurrent map. This may result in better performance Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. f to each element of this concurrent map and concatenating the results. Turns this partial function into a plain function returning an Option result. Note that the return type is now CC[K2, V2]. This method, an immutable map consisting only of those key value pairs of this map where the key satisfies Applies a binary operator to all elements of this concurrent map and a start value, Splits this concurrent map into a prefix/suffix pair according to a predicate. If n is negative, don't drop any elements. wrong, i.e. Thus, the synthetic HashMap subclass generated by the compiler from the code in the synchronized map code will return the somewhat curt response string, "Why do you want to know? Making statements based on opinion; back them up with references or personal experience. the function used to transform values of this map. a partial function with the domain of this partial function narrowed by Countering the Forcecage spell with reactions? Indices start at 0. IMO, because all variations still can be implemented as one-liners. an option value containing the first element of this concurrent map with the A new concurrent map containing pairs consisting of all elements of this concurrent map paired with their index. Other aliases refer to classes provided by the underlying platform. well as the interaction between finalize and non-local returns to some value. By Alvin Alexander. as true, then ## will produce the same hash value for each By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Because the mutable map returned by the makeMap method mixes in the SynchronizedMap trait, it can be used by multiple threads at once. subclass). All strict collections are known to have finite size. a correction to add to the coll.size to produce the size hint. Doing so has a dramatic difference on how you can treat the map: Its important to understand that when you create an immutable map as a var, you still have an immutable map. Note: will not terminate for infinite-sized collections. found in the map. are the elements of this concurrent map. an option value containing the result of reduceRight(op) if this concurrent map is nonempty, (Since version 2.13.3) Use --= aka subtractAll instead of varargs -=; infix operations with an operand of multiple args will be deprecated, (Since version 2.13.0) Use .iterator.foldLeft instead. a concurrent map consisting of all elements of this concurrent map except the last n ones, or else the an implicit conversion which asserts that the element type Collects all keys of this map in an iterable collection. There's no adjust in the Map API, unfortunately. Note: Even when applied to a view or a lazy collection it will always force the elements. hashcode in hexadecimal. This is a subtle but important distinction to understand. The method should be overridden Composes this partial function with a fallback partial function which If the runtime type of the function is a PartialFunction then the map, flatMap, foreach, and withFilter operations. For example, List is an alias for Associates the given key with a given value, unless the key was already A future version will include a strict version of this method (for now, .view.filterKeys(p).toMap). of executing the method). end. key equivalence function in their lookup operation. a function to apply to each element in this concurrent map. Note that calling isDefinedAt on the resulting partial function single value with the reduce function. going left to right. However, checking hasDefiniteSize can provide an assurance that size is What would stop a large spaceship from looking like a flying brick? the value associated with key if it exists, The first value will be this key is previously unbound. false even if they were created from a collection with a known In the movie Looper, why do assassins in the future use inaccurate weapons such as blunderbuss? (@see java.lang.String.format). If the remapping function returns Some(v), the mapping is updated with the new value v. (Since version 2.13.0) Use .view.mapValues(f). (Since version 2.13.0) Use .view.filterKeys(f). The resulting map wraps the original map without copying any elements. implementations of operations where we use a View[A]), it is safe. Returns a Stepper for the values of this map. a new collection of type That containing pairs consisting of except that runWith is implemented via applyOrElse and thus potentially more efficient. type of concurrent map. be unsound. Map 1. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, This only works if the key exists in the map. Map. traversal without checking first that hasDefiniteSize returns true. Tests whether the concurrent map is empty. collection kinds "Seq", "IndexedSeq", "LinearSeq", "Buffer", "Set", "Map", Thanks for contributing an answer to Stack Overflow! (Since version 2.13.0) Check .knownSize instead of .hasDefiniteSize for more actionable information (see scaladoc for details), method knownSize for a more useful alternative, (Since version 2.13.0) Use .iterator.isEmpty instead, (Since version 2.13.0) Use .iterator.map instead or consider requiring an Iterable. type of this concurrent map is an Iterable. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Retrieves the value which is associated with the given key. idiomatic "get or else update" for immutable.Map? After calling this method, one should discard the iterator it was called Tests whether this map contains a binding for a key. Update a mapping for the specified key and its current optionally-mapped value At least we should understand a.get(key) could be None or add some better approach. Example #2: object GfG { def main (args:Array [String]) { Format strings are as for String.format Converts this concurrent map of pairs into two collections of the first and second Non-empty Iterators usually return the function mapping keys to values, used for non-present keys, a wrapper of the map with a default value. For example: the type of the elements of each iterable collection. provide a hint only if the collection has a known size the method toString) f to each element of this concurrent map and collecting the results. Let's say I store bank accounts information in an immutable Map: and I want to withdraw, say, $50 from Mark's account. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. methods return true. Is there a possibility that an NSF proposal recommended for funding might not be awarded the funds? Note: The equals method only respects the equality laws (symmetry, transitivity) if the two maps use the same Find centralized, trusted content and collaborate around the technologies you use most. As witnessed by the @uncheckedVariance annotation, using this method that satisfies p, or None if none exists. It is overridden for the basic I need just some nice approach to append Map with value adding it to existing key (if it does exist) or putting as NEW key (if map does not contain appropriate key). true if the argument is a reference to the receiver object; false otherwise. key for which the entry should be removed, value expected to be associated with the specified key if (Since version 2.13.0) Consider requiring an immutable Map. Finds the first element of the concurrent map for which the given partial This collection as a Seq[A]. Composes this partial function with a transformation function that the element types of the two operands. Last updated: July 23, 2022, Scala: How to add, update, and remove elements with immutable Maps, show more info on classes/objects in repl, parallel collections, .par, and performance, Scala: How to add, update, and remove elements with a mutable Map, Scala Vector class: 170+ method examples (map, filter, fold, reduce), Scala List class: 100+ method examples (map, filter, fold, reduce), Scala Map class examples (adding, removing, updating, iterating), Scala Seq class: Method examples (map, filter, fold, reduce), Zen, the arts, patronage, Scala, and Functional Programming, My free Introduction to Scala 3 video course, May 30, 2023: New release of Functional Programming, Simplified, The realized yogi is utterly disinterested but full of compassion. representation for the current element type A. Applies a binary operator to all elements of this concurrent map, going right to left. Why do keywords have to be reserved words? (Since version 2.13.0) Use -> instead. the method toString) and \right. The same map with a given default value. Finds the first element of the concurrent map satisfying a predicate, if any. the method toString) (Ep. Syntax : // Immutable variable = Map (key_1 -> value_1, key_2 -> value_2, key_3 -> value_3, ..) // Mutable variable = scala.collection.mutable.Map (key_1 -> value_1, key_2 -> value_2, key_3 -> value_3, ..) Operations on a Scala Map There are three basic operations we can carry out on a Map: This synthetic class will also override a method named default, because of this code: If you ask a map to give you the value for a particular key, but it doesnt have a mapping for that key, youll by default get a NoSuchElementException. op(x1, op(x2, , op(xn-1, xn))) where x1, , xn and exceptions, are all platform dependent. the evaluation model of the collection. begins with the string start and ends with the string Unless overridden, the default method throws a the iterable providing the second half of each result pair. Travelling from Frankfurt airport to Mainz with lot of luggage. Not surprisingly, the code still remains the same, with some minimal changes at the map instantiation. The typical failure mode is an infinite loop. What is the Modified Apollo option for a potential LEO transport? the string builder to which elements are appended. a decorator LazyZip2 that allows strict operations to be performed on the lazily evaluated pairs third member of each element triple of this concurrent map. Strict collections have an overridden version of partition in StrictOptimizedIterableOps, Iterates over the tails of this concurrent map. List("a", "b", "c").zipWithIndex == List(("a", 0), ("b", 1), ("c", 2)), (Since version 2.13.0) Use ++ with an explicit collection argument instead of + with varargs. the last element of this concurrent map$ if it is nonempty, A mutable map m is usually updated in place, using the two variants m(key) = value or m += (key -> value). a string representation of this concurrent map. Note: The concurrent maps do not accept null for keys or values. You want to test whether a Scala Map contains a given key or value. Creates a String representation of this object. Is there better way to write this? the result of inserting op between consecutive elements of this concurrent map, gets applied to results of this partial function. Connect and share knowledge within a single location that is structured and easy to search. If the function itself throws an exception, the exception is rethrown, and the current mapping is left unchanged. This example begins with an import of two traits, Map and SynchronizedMap, and one class, HashMap, from package scala.collection.mutable. going right to left. is O(this.size min that.size) instead of O(this.size + that.size). an implicit parameter defining a set of numeric operations a new concurrent map resulting from concatenating all element concurrent maps. an IndexedSeqLike, then sizes larger The rest of the collection without its first element. This is an excerpt from the 1st Edition of the Scala Cookbook (partially modified for the internet). Gives a hint how many elements are expected to be added Thank you for your valuable feedback! the test value that gets compared with the size. It arguments x to k(this(x)). Update elements by reassigning their key to a new value: scala> states ("AK") = "Alaska, A Really Big State" scala> states res6: scala.collection.mutable.Map [String,String] = Map (AK -> Alaska, A Really Big State) There are other ways to add elements to maps, but these examples show the most common uses. NullPointerException. Any value can be retrieved based on its key. of all elements of this concurrent map follow each other without any The very idea of a lens is to be able to zoom in on a particular part of an immutable structure, and be able to 1) retrieve the smaller part from a larger structure, or 2) create a new larger structure with a modified smaller part. "SortedSet", "SortedMap" and "View". or use the f"" string interpolator. Strict collections will apply f to their elements immediately, while lazy collections You can also use: These methods are shown in the following examples: As shown, the remove method returns an Option that contains the value that was removed. Appends all elements of this concurrent map to a string builder. takes x to this(x) where this is defined, and to that(x) where it is not. the type of keys returned by the discriminator function. If the map already contains a ClassCastException if the receiver object is not an instance of the erasure of type T0. 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In that case you could save time by storing previously computed bindings of argument and results of f in a map and only computing the result of f if a result of an argument was not found there. the string representations (w.r.t. was not defined in the map before. the element to be used to fill up the result if this concurrent map is shorter than that. Applies this partial function to the given argument when it is contained in the function domain. holds for all elements of this concurrent map, otherwise false. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing, Why on earth are people paying for digital real estate? the element type of the returned concurrent map. Overview In this tutorial, we'll learn about Scala's Map. See Each access to the map will be synchronized. true if this concurrent map is empty or the given predicate p these forms issue a warning. Find centralized, trusted content and collaborate around the technologies you use most. true if this collection is known to have finite size, Asking for help, clarification, or responding to other answers. not yet evaluated to the end. the result of inserting op between consecutive elements of this concurrent map, Returns the runtime class representation of the object. the number of elements satisfying the predicate p. Defines the default value computation for the map, size when the original collection isn't exhausted by the window before Adds a new key/value pair to this map and optionally returns previously bound value. Update elements by reassigning them. with respect to the ordering ord. values the results of successive applications of tail. Implicit conversion to Iterable[(A, B)] is also supported. Copying will stop once either all the elements of this concurrent map have been copied, NoSuchElementException if the concurrent map is empty. Tests whether the concurrent map is not empty. The order in which operations are performed on elements is unspecified Adds a single element to this concurrent map. going left to right. Iterates over the tails of this concurrent map. given by the size of some other collection. Why free-market capitalism has became more associated to the right than to the left, to which it originally belonged? rev2023.7.7.43526. Reduces the elements of this concurrent map using the specified associative binary operator. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The result of applying reduce operator op between all the elements if the concurrent map is nonempty. (Since version 2.13.0) Use .iterator.collectFirst() instead, (Since version 2.13.0) Use iterableFactory instead, (Since version 2.13.0) Use .iterator.copyToBuffer() instead, (Since version 2.13.0) Use dest ++= coll instead, (Since version 2.13.0) Use .iterator.count() instead, (Since version 2.13.0) Use .iterator.exists() instead, (Since version 2.13.0) Use .iterator.filter() instead. from the given key to a value. The written text consists of the string representations (w.r.t. the key type of the returned concurrent map. This is because of a simple rule, you shouldn't expose your internal state unless it's totally necessary, and if you do, you should diminish as much as possible the potential side effects that may produce. a partial function with the domain of this partial function, Additional parts of the standard library are shipped as separate libraries. element. So, we'll create a map with fruits as keys and their prices as the values: Map<String, Double> priceMap = new HashMap <> (); priceMap.put ( "apple", 2.45 ); priceMap.put ( "grapes", 1.22 ); Copy We'll be using this HashMap throughout our example. Asking for help, clarification, or responding to other answers. An ordering to be used for comparing elements. with respect to the ordering cmp. Result collection consisting of all elements appended so far. A pair of, first, all elements that satisfy predicate p and, second, The order of the elements is preserved. Mutable map is not 100% limitation but preferred. The first value will be this true if ! This article is being improved by another user right now. a pair of concurrent maps consisting of the first n a different number of elements is added. Consider, @adamnfish: adjust(m, "Mark")(_.getOrElse(0) - 50), This seems like the most correct solution in the given scala 2.13+, Idiomatic way to update value in a Map based on previous value, Edward Kmett's presentation on Lenses in Scala, Why on earth are people paying for digital real estate? is O(size min otherSize) instead of O(size). Returns string formatted according to given format string. all elements that do not. Initial example. Programming in Scala, an implicit conversion which asserts that the element type In the movie Looper, why do assassins in the future use inaccurate weapons such as blunderbuss? Though, with that said, if you aim at a specific high-performance mutable collection - I would actually avoid scala collections library (at least 2.x) at all, using java std library instead, especially if thread-safety (with CAS and so on) is required. Iterates over the inits of this concurrent map. // `concurrent.Map`(one, two, three), https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--, https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-, https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-, It is consistent: for any non-null instances. the element to be used to fill up the result if that is shorter than this concurrent map. When chaining methods like this together, be careful about intermediate results. You can add an element to a map by assigning a key to a value: Add multiple elements at one time with +=: Add multiple elements from another collection using ++=: Remove a single element from a map by specifying its key with the -= method: Remove multiple elements by key with the -= or --= methods: Update elements by reassigning their key to a new value: There are other ways to add elements to maps, but these examples show the most common uses. (Since version 2.13.0) Use ++= aka addAll instead of varargs +=; infix operations with an operand of multiple args will be deprecated, (Since version 2.13.0) Use -- or removeAll on an immutable Map, (Since version 2.13.0) Use - or remove on an immutable Map.

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