Filter map for values of None

I've searched around a bit, but haven't found a good answer yet on how to filter out any entries into a map that have a value of None. Say I have a map like this:

val map = Map[String, Option[Int]]("one" -> Some(1), 
                                   "two" -> Some(2), 
                                   "three" -> None)

I'd like to end up returning a map with just the ("one", Some(1)) and ("two", Some(2)) pair. I understand that this is done with flatten when you have a list, but I'm not sure how to achieve the effect on a map without splitting it up into keys and values, and then trying to rejoin them.

Like every collection type in the scala.collection namespace a Map has the filter method defined and Optionhas the isDefined method, which is true for Some and false for None. You can filter out the Nonevalues by combining these two:

scala> map.filter(_._2.isDefined)
res4: scala.collection.immutable.Map[String,Option[Int]] = Map(one -> Some(1), two -> Some(2))

How to filter a Scala Map (filterKeys, retain, transform , your algorithm can test both the key and value of each element to decide which elements to retain in the map. In a related note, the transform� Hence, removal of None values in essential and knowledge of it is a must. Let’s discuss certain ways in which this is achieved. Method #1 : Naive Method In naive method, we iterate through the whole list and append all the filtered, non-None values into a new list, hence ready to be performed with subsequent operations.

If you're filtering out None values, you might as well extract the Some values at the same time to end up with a Map[String,Int]:

scala> map.collect { case (key, Some(value)) => (key, value) }
res0: scala.collection.immutable.Map[String,Int] = Map(one -> 1, two -> 2)

Maps, A Map is an Iterable consisting of pairs of keys and values (also named produce a new map by filtering and transforming bindings of an existing map. ms get k, The value associated with key k in map ms as an option, None if not found. Java 8 – Filter Map by both Keys and Values. In this example we are filtering a Map by keys and values both. When we filter a Map like this we are joining both the conditions by AND (&&) logical operator. You can also place both the conditions in the single filter() method and join them using any logical operator such as OR (||), AND(&&) or

Also map.filterKeys( map(_) != None)

or

for( (k,v) <- map if( v!= None)) yield (k,v)

This approach provides a general filterValues method that doesn't exist on maps. I miss such a method, because none of the alternatives is perfect.

[Updated later] This is a better version that doesn't do a lookup on each entry and still reads reasonably clearly.

map.filter( {case (x,y)=> y!=None})

Scala Map filter() method with example, Here, an empty map is returned as none of the elements satisfy the stated predicate. Check all the values you want to include in the expression. This option is only supported by the is any of and is none of conditions. Multiple (predefined) —Filter based on multiple values that users can select in a static list that you define. By default, Ask for values is checked and the list is set to show values based on the previous

Template Designer Documentation — Jinja Documentation (2.11.x), If a variable or attribute does not exist, you will get back an undefined value. Filters are separated from the variable by a pipe symbol ( | ) and may have optional arguments in parentheses. If ignore missing is given, it will fall back to rendering nothing if none of the Perform a sequence / mapping containment test. Map, reduce, and filter are all array methods in JavaScript. Each one will iterate over an array and perform a transformation or computation. Each will return a new array based on the result of the function. In this article, you will learn why and how to use each one. Here is a fun summary by Steven Luscher: > Map/filter/reduce in a tweet: map([🌽, 🐮, 🐔], cook

Array.prototype.filter(), The following example uses filter() to create a filtered array that has all elements with values less than 10 removed. function isBigEnough(value) {� If you’re starting in JavaScript, maybe you haven’t heard of .map(), .reduce(), and .filter().For me, it took a while as I had to support Internet Explorer 8 until a couple years ago.

Built-in Functions — Python 3.8.5 documentation, Return a Boolean value, i.e. one of True or False . x is converted using the latter case, expression statements that evaluate to something other than None will be printed). See dict and Mapping Types — dict for documentation about this class. Note that filter(function, iterable) is equivalent to the generator expression� Hash_Map.values() Parameters: The method does not accept any parameters. Return Value: The method is used to return a collection view containing all the values of the map. Below programs are used to illustrate the working of java.util.HashMap.values() Method: Program 1: Mapping String Values to Integer Keys.

Comments
  • Neato. I wouldn't have guessed the syntax though. Still a little confused on _. From what I understand, we're telling it to go to the second item (the value) of the first (current) pair?
  • @KChaloux In this case _ refers to the first argument of a function literal being passed to the filter method. It's a shorthand for x => x._2.isDefined
  • And the _2 comes from the Tuple.