Scala – How to access value of map with a key if key was not found in scala

scala

Assume I have

var mp = Map[String,String]()

.....

val n = mp("kk")

The above will throw runtime error in case key "kk" did not exist.

I expected n will be null in case key did not exist. I want n to be null if key did not exist.

What is the proper way to handle this situation in scala with a short code sample?

Best Solution

First of all, you probably don't really want null, as that's almost always a sign of bad coding in Scala. What you want is for n to be of type Option[String], which says that the value is either a String or is missing. The right way to do that is with the .get() method on you map

val n = mp.get("kk")

If you really do need null (for interop with Java libraries, for example), you can use .getOrElse()

val n = mp.getOrElse("kk", null)

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Scala – How to iterate scala map

Three options:

attrs.foreach( kv => ... )          // kv._1 is the key, kv._2 is the value
attrs.foreach{ case (k,v) => ... }  // k is the key, v is the value
for ((k,v) <- attrs) { ... }        // k is the key, v is the value

The trick is that iteration gives you key-value pairs, which you can't split up into a key and value identifier name without either using case or for.

Scala – Elegant way handling both missing key and null values from Scala Map

If you're dealing with an immutable Map, the safest thing to do would be to filter out all the null values up front (this incurs the creation of yet another Map instance, but unless you have a specific reason to care about performance here it should not be an issue).

val withoutNulls = map.filter{case (k,v)=> v != null}

Any key that was holding a null is gone, and as such getOrElse on this key will return None. Trivial, and does the job once for all.

Best Solution

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Scala – How to iterate scala map

Scala – Elegant way handling both missing key and null values from Scala Map

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