High-order functions of the Scala language (4)

==> Common function explanation

---> Map acts on each element of the list

Define a list of Val list= list (1,2,3,4,5,6,7,8,9)//list all elements in the list by multiplying 2list.map ((i:int) + i*2)//using foreach to do the same operation, foreach does not return Value List.foreach ((i:int) = i*2)

---> Filter filters return an element with a value of False

Val list = list (1,2,3,4,5,6,7,8,9) List.filter ((i:int) = i%2==0)//Return result: list[int] = List (2, 4, 6, 8)//can also write Num.filter ( _%2==0)

---> Zip combines two numbers and

List (4,5,6)///output is list[(int, int)] = List ((1,4), (2,5), (3,6))

---> Partition place elements that conform to the filtering rules in one partition, placing them in a partition that does not conform to the filter rules

List (1,2,3,4,5,6,7,8,9). partition ((I:int) and i%2==0)//Output results are: (List[int], list[int]) = (List (2, 4, 6, 8), List (1, 3, 5, 7 , 9))

---> Find finds the first rule-compliant element in a list

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list (List (1,list), 2,3,4 (list ( list), List (5,6,7)). 8,9   If you want to continue the flattening operation, you will get an error List (list (1,list (2,3,4)),  list (list (5,6,7), List (8,9)) .flatten.flattenerror:< console>:12: error: no implicit view available from any =>  SCALA.COLLECTION.GENTRAVERSABLEONCE[B]. List (list (1,list (2,3,4)),  list (list (5,6,7), List (8,9)) .flatten.flatten//  to continue the flattening operation, you need to modify the processing process to List ( List (list (1), List (2,3,4)),  list (list (5,6,7), List (8,9))) .flatten.flatten//  result:list[int] =  List (1, 2, 3, 4, 5, 6, 7, 8, 9) 

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---> FLATMAP equivalent to a combination of two functions of Map and flatten

Val list = list (4,5,6)//The x here is equivalent to flatten the source data, then operates on each element List.flatmap (X=>x.map (_*2))// This clause is equivalent to the following two-step operation val x = List.flattenx.map (_*2)

Nesting of ==> closure functions

---> Define common functions:

def myfun (X:int, y:int): Int = x * y

---> use closures

Define a closure function, where x is a multiplier factor, which is multiplied by multiples (I understand it as a multiplier), Y is the parameter passed in using the function Def myfun (x:int) = (y:int) + x * y//First step defines the model of its own function val mytest = Myf UN (2)//Use your own defined function model, pass in Parameter mytest (20)

==> currying The name of a mathematician whose essence is to convert a multi-parameter function into a function chain with a single parameter function on each node

Example:

def add (X:int, y:int): Int = x + ydef Add (x:int) (Y:int) = x + y

High-order functions of the Scala language (4)