1, array
1) Create arrays
Create fixed-length arrays and variable-length arrays
//Create a fixed-length array, use the new keyword, specify that the array generic type is Int, the length is 5, the default will initialize these five values for the default value of the specified type, such as Int, then the five default values are all 0. //Note: If new, it's equivalent to calling the array's apply method to assign values directly to the array scala> val arr = new Array[Int](5) arr: Array[Int] = Array(0, 0, 0, 0, 0) //Modify the values of array elements scala> arr(0) res16: Int = 0 scala> arr(0) = 1 scala> arr(1) = 2 scala> arr(2) = 3 scala> arr res20: Array[Int] = Array(1, 2, 3, 0, 0) //Direct creation of fixed-length arrays and initialization of elements scala> val arr2 = Array(1,2,3,4,5) arr2: Array[Int] = Array(1, 2, 3, 4, 5) scala> arr2 res21: Array[Int] = Array(1, 2, 3, 4, 5) //Print arrays, by default hashcode, and toBuffer prints array elements scala> println(arr) [I@6c06b1bc scala> println(arr.toBuffer) ArrayBuffer(1, 2, 3, 0, 0) //Note the following because there is a difference between using new scala> val a = Array[Int](10) a: Array[Int] = Array(10) a.length = 1 scala> val b = new Array[Int](10) b: Array[Int] = Array(0, 0, 0, 0, 0, 0, 0, 0, 0, 0) a.length = 10
//Create Array Buffer as an Array (using the Array Buffer cache)
scala> val ab = new ArrayBuffer[Int]()
//The prompt is earlier than the ArrayBuffer type and needs a guide.
<console>:7: error: not found: type ArrayBuffer
val ab = new ArrayBuffer[Int]()
^
//Press tab key to give a prompt
scala> import scala.collection.mutable.Array
ArrayBuffer ArrayBuilder ArrayLike ArrayOps ArraySeq ArrayStack
//Package completion
scala> import scala.collection.mutable.ArrayBuffer
import scala.collection.mutable.ArrayBuffer
//Create a variable-length array of new ArrayBuffer[Int] () or do not require a new keyword
ArrayBuffer[Int]()，Now that it's getting longer, there's no need to specify the length.
scala> val ab = new ArrayBuffer[Int]()
ab: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()
//Adding one or more elements to an array+=
scala> ab += 1
res24: ab.type = ArrayBuffer(1)
scala> ab += 2
res25: ab.type = ArrayBuffer(1, 2)
//Add multiple elements
scala> ab += (3,4,5)
res26: ab.type = ArrayBuffer(1, 2, 3, 4, 5)
scala> ab
res27: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3, 4, 5)
2) Array operation
//Array additive variable length and fixed length can also be used together.++= //Two variable-length arrays are added, and the elements in ac are added to ab scala> ab ++= ac res32: ab.type = ArrayBuffer(1, 2, 3, 4, 5, 1, 2, 3, 4, 5) scala> ab res33: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3, 4, 5, 1, 2, 3, 4, 5) //Add fixed-length array elements to variable-length array ac scala> ac ++= Array(6,7,8) res34: ac.type = ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8) scala> ac res35: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8) //Insert elements at specified positions in the array, using insert //Insert two 9 at the corner of the ac array labeled 1 scala> ac.insert(1,9,9) scala> ac res38: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 9, 9, 2, 3, 4, 5, 6, 7, 8) //Insert two 9 into the position marked 0 by ac angle scala> ac.insert(0,9,9) scala> ac res40: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(9, 9, 1, 9, 9, 2, 3, 4, 5, 6, 7, 8) //Delete the element at the specified location of the array, using remove //Delete 2 elements from the position marked 0 by ac scala> ac.remove(0,2) scala> ac res42: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 9, 9, 2, 3, 4, 5, 6, 7, 8) scala> ac.remove(1,2) scala> ac res44: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8)
3) traversal array
Use the for loop and until
Useful until generates footmarks, 0 until 10 contains 0 and does not contain 10
scala> 0 until 10 res47: scala.collection.immutable.Range = Range(0, 1, 2, 3, 4, 5, 6, 7, 8, 9) //Variable array scala> for(i <- 0 until ac.length) print (ac(i) + " ") 1 2 3 4 5 6 7 8
4) Array Conversion
The field keyword converts the original array to produce a new array, with the original array unchanged
scala> val arr = Array(1,2,3,4,5,6,7,8,9) arr: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9) //Put each element in arr multiplied by 10 into a new array scala> val arr2 = for (i <- arr) yield i * 10 arr2: Array[Int] = Array(10, 20, 30, 40, 50, 60, 70, 80, 90) scala> arr2 res0: Array[Int] = Array(10, 20, 30, 40, 50, 60, 70, 80, 90) //It's more convenient to use map scala> val arr3 = arr.map(_ * 10) arr3: Array[Int] = Array(10, 20, 30, 40, 50, 60, 70, 80, 90) scala> arr3 res2: Array[Int] = Array(10, 20, 30, 40, 50, 60, 70, 80, 90) //perhaps scala> val arr4 = arr.map(x => x * 10) arr4: Array[Int] = Array(10, 20, 30, 40, 50, 60, 70, 80, 90)
Use filters
scala> val arr2 = for( i <- arr if i % 2 == 0) yield i * 2 arr2: Array[Int] = Array(4, 8, 12, 16) //It's not good to use map directly for the above situation, because there are filtering conditions, so filter is used here. scala> val arr5 = arr.filter(x => x % 2 ==0) arr5: Array[Int] = Array(2, 4, 6, 8) scala> val arr5 = arr.filter(x => x % 2 ==0).map(x => x * 2) arr5: Array[Int] = Array(4, 8, 12, 16) scala> arr5 res6: Array[Int] = Array(4, 8, 12, 16) //Or use as a simpler way of writing scala> val arr6 = arr.filter(_ % 2 ==0).map(_ * 2) arr6: Array[Int] = Array(4, 8, 12, 16) scala> arr6 res7: Array[Int] = Array(4, 8, 12, 16)
5) Array Common Algorithms
//Array maximum, minimum, sum scala> arr.sum res18: Int = 41 scala> arr.max res19: Int = 9 scala> arr.min res20: Int = 1 //Some Methods of Array Sorting scala> val arr = Array(3,1,6,8,5,4,9,2,3) arr: Array[Int] = Array(3, 1, 6, 8, 5, 4, 9, 2, 3) scala> arr.sorted res9: Array[Int] = Array(1, 2, 3, 3, 4, 5, 6, 8, 9) scala> arr res10: Array[Int] = Array(3, 1, 6, 8, 5, 4, 9, 2, 3) scala> val arr2 = arr.sorted arr2: Array[Int] = Array(1, 2, 3, 3, 4, 5, 6, 8, 9) scala> arr2 res11: Array[Int] = Array(1, 2, 3, 3, 4, 5, 6, 8, 9) scala> val arr2 = arr.sorted.reverse arr2: Array[Int] = Array(9, 8, 6, 5, 4, 3, 3, 2, 1) scala> arr2 res12: Array[Int] = Array(9, 8, 6, 5, 4, 3, 3, 2, 1) scala> arr.sortBy(x => x) res13: Array[Int] = Array(1, 2, 3, 3, 4, 5, 6, 8, 9) scala> arr.sortWith(_>_) res14: Array[Int] = Array(9, 8, 6, 5, 4, 3, 3, 2, 1) scala> arr.sortWith(_<_) res15: Array[Int] = Array(1, 2, 3, 3, 4, 5, 6, 8, 9) scala> arr.sortWith((x,y)=> x<y) res16: Array[Int] = Array(1, 2, 3, 3, 4, 5, 6, 8, 9) scala> arr.sortWith((x,y)=> x>y) res17: Array[Int] = Array(9, 8, 6, 5, 4, 3, 3, 2, 1)
2, mapping
In Scala, the data structure of hash tables is called Mapping
1) Create mappings
//The first way to create it is to use "->" a - > b as if a is the key B is the value
scala> val props = Map(1 -> 23,2 -> 45)
//In the case of java, both key and value types are Int
props: scala.collection.immutable.Map[Int,Int] = Map(1 -> 23, 2 -> 45)
scala> val props = Map("user" -> "admin", "pwd" -> "1234")
//In java, both key and value types are String
props: scala.collection.immutable.Map[String,String] = Map(user -> admin, pwd -> 1234)
//The second way to create it is to use (k,v)
scala> val map = Map((1,"tom"),(2,"jack"))
map: scala.collection.immutable.Map[Int,String] = Map(1 -> tom, 2 -> jack)
scala> val name = map(1)
name: String = tom
2. Getting and modifying values in maps
//Value by key
scala> val name = map(1)
name: String = tom
//Modified values are not found, because the Map above is immutable and needs to be re-imported.
scala> map(1) = "lucy"
<console>:9: error: value update is not a member of scala.collection.immutable.Map[Int,String]
map(1) = "lucy"
//Re-importing map packages with variable values can modify elements successfully
scala> import scala.collection.mutable.Map
Map MapBuilder MapLike MapProxy
scala> import scala.collection.mutable.Map
import scala.collection.mutable.Map
scala> val map = Map((1,"tom"),(2,"jack"))
map: scala.collection.mutable.Map[Int,String] = Map(2 -> jack, 1 -> tom)
scala> map(1) = "lucy"
scala> map
res25: scala.collection.mutable.Map[Int,String] = Map(2 -> jack, 1 -> lucy)
//Adding elements to maps
scala> map += ((3,"wangw"),(4,"lining"))
res26: map.type = Map(2 -> jack, 4 -> lining, 1 -> lucy, 3 -> wangw)
scala> map += (5 -> "xiaox",6 -> "jiej")
res27: map.type = Map(2 -> jack, 5 -> xiaox, 4 -> lining, 1 -> lucy, 3 -> wangw, 6 -> jiej)
//In addition, if k is the same, then v will be overwritten, and the corresponding xiaox of hair 5 will be modified to xiao.
scala> map += (5 -> "xiao")
res28: map.type = Map(2 -> jack, 5 -> xiao, 4 -> lining, 1 -> lucy, 3 -> wangw, 6 -> jiej)
//Addition of two maps++=
scala> val map2 = Map((1,"laowang"),(2,"lisi"))
map2: scala.collection.mutable.Map[Int,String] = Map(2 -> lisi, 1 -> laowang)
scala> val map3 = Map(3 ->"jinbm")
map3: scala.collection.mutable.Map[Int,String] = Map(3 -> jinbm)
//When added, if k is the same, v will cover, and the elements in map 3 will be added to map 2.
scala> map2 ++= map3
res33: map2.type = Map(2 -> lisi, 1 -> laowang, 3 -> jinbm)
scala> map2
res34: scala.collection.mutable.Map[Int,String] = Map(2 -> lisi, 1 -> laowang, 3 -> jinbm)
Note: If you can't get v based on k in the mapping, you will report an error.
scala> map2(4)
java.util.NoSuchElementException: key not found: 4
at scala.collection.MapLike$class.default(MapLike.scala:228)
at scala.collection.AbstractMap.default(Map.scala:58)
...
//Use getOrElse to solve this problem. If you can't find the v corresponding to this k, give it a default value.
scala> map2.getOrElse(4,0)
res36: Any = 0
Print Narcissus Number
(100 to 999).filter(x => {pow(x%10,3) + pow(x/10%10,3) + pow(x/100,3) == x}).foreach(println)