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Functional Programming in Scala
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//Currying is when you break down a function that takes multiple arguments into a //series of functions that take part of the arguments. | |
//converts a function f of two arguments into a function of one argument that partially applies f. | |
def curry[A,B,C](f: (A,B) => C): A => (B => C) = | |
(a: A) => (b: B) => f(a,b) | |
//> curry: [A, B, C](f: (A, B) => C)A => (B => C) |
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//in javascript | |
//A loop - prints "1 2 3" to console | |
var res = 0 | |
let nums = [1, 2, 3] | |
for(i=0; i<nums.length; i++) { | |
res = res + nums[i] | |
} | |
//Another loop - Performs 1+2+3 then print out sum | |
var res = "" | |
let strs = ["a", "b", "c"] | |
for(i=0; i< strs.length; i++) { | |
res = res + strs[i] | |
} |
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[1,2,3].reduce((a,b) => (a+b), 0) //> 6 | |
["a", "b", "c"].reduce((a,b) => a+b, "") //> "abc" |
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const myReduce = (arr, initVal) => | |
arr.reduce((a,b) => (a+b), initVal) | |
let arr1 = [1,2,3] | |
let arr2 = ["a", "b", "c"] | |
myReduce(arr1, 0) //> 6 | |
myReduce(arr2, "") //>"abc" |
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let arr3 = [arr1, arr2] | |
myReduce(arr3, []) |
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let arr3 = [arr1, arr2] | |
arr3.reduce((a,b) => a.concat(b), []) |
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//In Scala | |
List(1,2,3) ++ List("a", "b", "c") //> res: List[Any] = List(1, 2, 3, a, b, c) | |
List(1,2,3) ++ "abc" //> res: List[AnyVal] = List(1, 2, 3, a, b, c) | |
"abc" ++ List(1,2,3) //res: scala.collection.immutable.IndexedSeq[AnyVal] = Vector(a, b, c, 1, 2, 3) | |
"abc" ++ "def" //> res: String = abcdef | |
"abc" + "def" //> res: String = abcdef |
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//In javascript | |
let arr1 = [""] | |
let arr2 = ["", ""] | |
let arr3 = ["", "", "a"] | |
let res1 = arr1.reduce((a,b) => a+b) //> "" | |
let res2 = arr2.reduce((a,b) => a+b) //> "" | |
let res3 = arr3.reduce((a,b) => a+b) //> "a" | |
const strLen = arr => | |
arr.reduce((a,b) => a+b).length | |
strLen([res1]) //> 0 | |
strLen([res1, res2]) //> 0 | |
strLen([res1, res2, res3]) //> 1 | |
strLen([res3, res2, res1]) //> 1 |
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def findAve(l: List[Double]): Double = l.reduce(_ + _)/l.length | |
findAve(List(1,2,3)) |
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//In javascript | |
let num = "7" //user inputs "7" for num | |
let res = num - 1 //> 6 ... good | |
let num = "07" //user inputs "07" for num | |
res = num - 1 //>6 ... still good | |
let num = "apple" - 1 //> NaN | |
res = num - 1 //> NaN ... bad |
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def findAve(l: List[Double]) = l.reduce(_ + _)/l.length | |
//> findAve: (l: List[Double])Double |
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//In javascript | |
let findAve = arr => arr.reduce((a,b) => a+b)/arr.length | |
findAve([1,2,3]) //> 2 | |
findAve([1,1,3]) //>1.6666666666666667 |
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//In Scala | |
def findAve(l: List[Int]) = l.reduce(_ + _)/l.length | |
//> findAve: (l: List[Int])Int | |
findAve(List(1,2,3)) //> 2 | |
findAve(List(1,1,3)) //> 1 | |
def findAve2(l: List[Int]): Double = l.reduce(_ + _)/l.length | |
findAve2(List(1,1,3)) //> 1.0 | |
def findAve3(l: List[Double]): Double = l.reduce(_ + _)/l.length | |
findAve: (l: List[Double])Double | |
findAve(List(1,1,3)) //>1.6666666666666667 |
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//In Java | |
double[] arr = new double[] {1,2,3}; | |
double acc = 0; | |
for(int i=0; i<arr.length; i++) { | |
acc += arr[i]; | |
} | |
double ave = acc/arr.length; | |
System.out.println("The average of " + Arrays.toString(arr) + " is "+ave); | |
//> The average of [1.0, 2.0, 3.0] is 2.0 |
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//In Scala | |
def list = List(1.0, 2.0 ,3.0) | |
def findAve(l: List[Double]): Double = l.reduce(_ + _)/l.length | |
findAve(List(1,2,3)) | |
println(s"The average of $list is $ave") | |
//> The average of List(1.0, 2.0, 3.0) is 2.0 |
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