# Scala Tips for updateStateByKey

In the previous section on udateStateByKey, following we need to brush up some Scala methods:

Specifically:

```
val updateFunc = (values: Seq[Int],state: Option[Int])=>{
val currentCount = values.foldLeft(0)(_+_)
val previousCount = state.getOrElse(0)
Some(currentCount + previousCount)
}
```

A few methods we need to discuss here:

#### values.foldLeft(0)(\_+\_)

In fact, there are follow fold\* methods for any collections (such as List): 

fold(Initial:T)(func) 

foldLeft(Initial:T)(func) 

foldRight(Initial:T)(func)

*Tips: fold methods above are very similar to reduce method, except fold methods allow a initial value as argument, while reduce does not*.

#### state:Option\[Int]

this means argument state is an integer, but can be None. In Scala, it is denoted as Option\[Int]

If a variable in Scala may be None in value, it must be declared as Option\[T] (T is a datatype placeholder, such as Int, String etc)

An Option\[T] can be either Some\[T] or None object, which represents a missing value.

If a variable needs to be computed with, for example having data type  Option\[Int], to avoid computing a None value, an Optional variable has a method called getOrElse(default value), such as

state.getOrElse(0)

For the above function updateFunc, let's test it:

```
val updateFunc = (values: Seq[Int],state: Option[Int])=>{
val currentCount = values.foldLeft(0)(_+_)
val previousCount = state.getOrElse(0)
currentCount + previousCount
}

```

Then create a list x, and y:Option\[Int], assigned to None, then call updateFunc

```
val x=Seq(1,2,3,4,5)
val y:Option[Int]=None
updateFunc(x,y)

/*Output
15
*/

```

Now, replace foldLeft(0)(\_+\_) with fold(0)(\_+\_), foldRight(0)(\_+\_) and reduce(\_+\_), and test them to reinforce understanding.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://george-jen.gitbook.io/data-science-and-apache-spark/scala-tips-for-updatestatebykey.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.