# Partial Functions in Scala

Introduction:
When a function is not able to produce a return for every single variable input data given to it then that function is termed as Partial function. It can determine an output for a subset of some practicable inputs only. It can only be applied partially to the stated inputs.
Some important points:

• Partial functions are beneficent in understanding many inconsistent kind of Scala functions.
• It can be interpreted by utilizing case statements.
• It is a Trait, which needs two methods namely isDefinedAt and apply to be implemented.

Example:

 `// Scala program of  ` `// Partial function ` ` `  `// Creating object  ` `object` `Case ` `{ ` ` `  `    ``// Main method ` `    ``def` `main(args``:` `Array[String]) ` `    ``{ ` ` `  `        ``// Creating Partial function  ` `        ``// using two methods ` `        ``val` `r ``=` `new` `PartialFunction[Int, Int]  ` `        ``{ ` ` `  `            ``// Applying isDefinedAt method  ` `            ``def` `isDefinedAt(q``:` `Int) ``=` `q !``=` `0` ` `  `            ``// Applying apply method ` `            ``def` `apply(q``:` `Int) ``=` `12` `* q ` ` `  `        ``}  ` ` `  `        ``// Displays output if the ` `        ``// condition is satisfied ` `        ``println(r(``10``)) ` `    ``} ` `} `

Output:

```120
```

Here, two methods are defined for applying Partial function, where isDefinedAt states the condition and apply performs the operation if the given condition is satisfied.
Methods to define Partial functions:
There are some methods to define Partial function, which includes case statements, collect method, andThen, and orElse.

• Partial function using Case statement:
we will create a Partial function below using case statement.
Example:

 `// Scala program using ` `// case statements ` ` `  `// Creating object  ` `object` `Case ` `{ ` ` `  `    ``// Main method ` `    ``def` `main(args``:` `Array[String]) ` `    ``{ ` ` `  `        ``// Creating Partial function ` `        ``val` `d``:` `PartialFunction[Int, Int] ``=` `        ``{ ` ` `  `            ``// using case statement  ` `            ``case` `x ``if` `(x ``%` `3``) ``==` `0` `=>` `x * ``3` `        ``} ` ` `  `        ``// Displays output if  ` `        ``// the condition is  ` `        ``// satisfied ` `        ``println(d(``3``)) ` `    ``} ` `} `

Output:

```9
```

Here, Partial function is created using case statement so, apply and isDefinedAt is not required here.

• Partial function using orElse:
This method is helpful in chaining Partial functions together.
Example:

 `// Scala program using ` `// orElse ` ` `  `// Creating object  ` `object` `orElse ` `{ ` ` `  `    ``// Main method ` `    ``def` `main(args``:` `Array[String]) ` `    ``{ ` ` `  `        ``// Creating Partial function1 ` `        ``val` `M``:` `PartialFunction[Int, Int] ``=`  `        ``{ ` ` `  `            ``// using case statement  ` `            ``case` `x ``if` `(x ``%` `5``) ``==` `0` `=>` `x * ``5` `        ``} ` ` `  `        ``// Creating Partial function2  ` `        ``val` `m``:` `PartialFunction[Int, Int] ``=`  `        ``{ ` ` `  `            ``// using case statement  ` `            ``case` `y ``if` `(y ``%` `2``) ``==` `0` `=>` `y * ``2` `        ``} ` ` `  `        ``// chaining two partial  ` `        ``// functions using orElse  ` `        ``val` `r ``=` `M orElse m ` ` `  `        ``// Displays output for  ` `        ``// which the given condition  ` `        ``// is satisfied ` `        ``println(r(``5``)) ` `        ``println(r(``4``)) ` `    ``} ` `} `

Output:

```25
8
```

Here, orElse will return output for which the given condition is satisfied.

• Partial function using Collect method:
Collect method requests Partial function to every single element of the collection and thus, helps in constructing a new collection.
Example:

 `// Scala program using ` `// collect method ` ` `  `// Creating object  ` `object` `Collect ` `{ ` ` `  `    ``// Main method ` `    ``def` `main(args``:` `Array[String]) ` `    ``{ ` ` `  `        ``// Creating Partial function ` `        ``val` `M``:` `PartialFunction[Int, Int] ``=`  `        ``{ ` ` `  `            ``// using case statement  ` `            ``case` `x ``if` `(x ``%` `5``) !``=` `0` `=>` `x * ``5` `        ``} ` ` `  `        ``// Applying collect method ` `        ``val` `y ``=` `List(``7``, ``15``, ``9``) collect { M } ` ` `  `        ``// Displays output for which  ` `        ``// the given condition  ` `        ``// is satisfied ` `        ``println(y) ` `    ``} ` `} `

Output:

```List(35, 45)
```

Here, Collect will apply Partial function to all the elements of the List and will return a new List on the basis of the conditions stated.

• Partial function using andThen:
This method appends at the end of the chains, which is utilized to continue towards additional chains of Partial functions.
Example:

 `// Scala program using ` `// andThen method ` ` `  `// Creating object  ` `object` `andThen ` `{ ` ` `  `    ``// Main method ` `    ``def` `main(args``:` `Array[String]) ` `    ``{ ` ` `  `        ``// Creating Partial function ` `        ``val` `M``:` `PartialFunction[Int, Int] ``=` `        ``{ ` ` `  `            ``// using case statement  ` `            ``case` `x ``if` `(x ``%` `4``) !``=` `0` `=>` `x * ``4` `        ``} ` ` `  `        ``// Creating another function ` `        ``val` `append ``=` `(x``:` `Int) ``=>` `x * ``10` ` `  `        ``// Applying andThen method  ` `        ``val` `y ``=` `M andThen append ` ` `  `        ``// Displays output after  ` `        ``// appending the another ` `        ``// function given ` `        ``println(y(``7``)) ` `    ``} ` `} `

Output:

```280
```

Here, andThen will append the output of Partial function with the another function given and then will return that value.

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