1, the array

1.1 Fixed-length arrays

  • A fixed-length array means that the length of the array is not allowed to change
  • The elements of an array can be changed

grammar

// Define the array by specifying the length
val/varThe variable name =new Array[Element type](Array length)// Initialize arrays directly with elements
val/varThe variable name =Array(element1Elements,2Elements,3...)
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Reference code

// Define the array by specifying the length
scala> val a = new Array[Int] (5)
a: Array[Int] = Array(0.0.0.0.0)

scala> a(0) = 110

scala> println(a(0))
110
// Initialize arrays directly with elements
// Define an array containing jave, Scala, and Python elements
scala> val a = Array("java"."scala"."python")
a: Array[String] = Array(java, scala, python)

scala> a.length
res17: Int = 3
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1.2 Variable-length arrays

Variable-length arrays are arrays of variable length that can be added or removed

1.2.1 Define variable-length arrays

Create an array of variable length, need to advance import ArrayBuffer class import scala. Collection. The mutable. ArrayBuffer

grammar

  • Create an empty ArrayBuffer variable length array.

    val/var a = ArrayBuffer[Element type]()Copy the code

  • Creates an ArrayBuffer with initial elements

    val/var a = ArrayBuffer(element1Elements,2Elements,3....).Copy the code

The sample

// Define an integer variable length array of length 0
val a = ArrayBuffer[Int] ()// Define a variable length array containing the contents
scala> val a = ArrayBuffer("hadoop"."storm"."spark")
a: scala.collection.mutable.ArrayBuffer[String] = ArrayBuffer(hadoop, storm, spark)
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1.2.2 Add/Modify/Delete Elements

  • use+ =Add elements
  • use- =Remove elements
  • use+ + =Appends an array to a variable-length array

The sample

// Define variable-length arrays
scala> val a = ArrayBuffer("hadoop"."spark"."flink")
a: scala.collection.mutable.ArrayBuffer[String] = ArrayBuffer(hadoop, spark, flink)

// Appends an element
scala> a += "flume"
res10: a.type = ArrayBuffer(hadoop, spark, flink, flume)

// Delete an element
scala> a -= "hadoop"
res11: a.type = ArrayBuffer(spark, flink, flume)

// Appends an array
scala> a ++= Array("hive"."sqoop")
res12: a.type = ArrayBuffer(spark, flink, flume, hive, sqoop)
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1.3 Go through the number group

The array can be traversed in two ways:

  • Use the for expression to iterate directly over the elements in the array

  • Iterate over the elements in a group using an index

Reference code

// Use the 'for expression' to iterate over the elements of the array directly
scala> val a = Array(1.2.3.4.5)
a: Array[Int] = Array(1.2.3.4.5)

scala> for(i<-a) println(i)
1
2
3
4
5

// Use 'index' to iterate over the elements in the array
1,0To n -- contains0, also including n scala>for(i <- 0 to a.length - 1) println(a(i))
1
2
3
4
5
2,0Until n -- Generates a series of numbers containing0, not including n scala>for(i <- 0 until a.length) println(a(i))

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1.4 Common algorithms for arrays

Arrays in Scala encapsulate common computation operations that we don’t need to re-implement ourselves when processing data in the future. Here are some commonly used algorithms:

  • Sum — sum method
  • Find the maximum — Max method
  • Find the minimum — min method
  • Sort — The sorted method

1.4.1 sum

The sum method in the array adds up all the elements to get the result

The sample

scala> val a = Array(1.2.3.4)
a: Array[Int] = Array(1.2.3.4)
/ / sum
scala> a.sum
res49: Int = 10
/ / Max
scala> a.max
res50: Int = 10
/ / the minimum
scala> a.min
res51: Int = 1
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1.4.2 sorting

The sorted array method, which sorts an array in ascending order. The Reverse method, on the other hand, reverses the array to sort in descending order

The sample

// Ascending sort
scala> a.sorted
res53: Array[Int] = Array(1.2.4.4.10)

/ / descending
scala> a.sorted.reverse
res56: Array[Int] = Array(10.4.4.2.1)
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