I have a array
[1,2,2,3,4,6,2,4,6,8,2,3,5]
I want to iterate over this array using a for loop to get a collection of tuples of adjacent elements. How should I code in Scala?
Expected output :
1-2|2-2|2-3|3-4|4-6|6-2|2-4|4-6|6-8|8-2|2-3|3-5
If you want the output like 1-2|2-2|2-3|3-4|........ as you mentioned in your comment you can try following,
val arr = Array(1,2,2,3,4,6,2,4,6,8,2,3,5)
//here first separate array elements by - then whole array by |
val str = arr.sliding(2).map(_.mkString("-")).mkString("|")
print(str)
//output
//1-2|2-2|2-3|3-4|4-6|6-2|2-4|4-6|6-8|8-2|2-3|3-5
In scala you have sliding function for that.
scala> val arr = Array(1,2,2,3,4,6,2,4,6,8,2,3,5)
arr: Array[Int] = Array(1, 2, 2, 3, 4, 6, 2, 4, 6, 8, 2, 3, 5)
scala> arr.sliding(2).foreach(tuple => println(tuple.mkString(" ")))
1 2
2 2
2 3
3 4
4 6
6 2
2 4
4 6
6 8
8 2
2 3
3 5
scala> arr.sliding(2).map(tuple => tuple.mkString("-")).mkString("|")
res10: String = 1-2|2-2|2-3|3-4|4-6|6-2|2-4|4-6|6-8|8-2|2-3|3-5
Related
Find a number available in first array with numbers in second. If number not found get the immediate lower.
val a = List(1,2,3,4,5,6,7,8,9)
val b = List(1,5,10)
expected output after comparing a with b
1 --> 1
2 --> 1
3 --> 1
4 --> 1
5 --> 5
6 --> 5
7 --> 5
8 --> 5
9 --> 5
Thanks
You can use TreeSet's to() and lastOption methods as follows:
val a = List(1, 2, 3, 4, 5, 6, 7, 8, 9)
val b = List(1, 5, 10)
import scala.collection.immutable.TreeSet
// Convert list `b` to TreeSet
val bs = TreeSet(b.toSeq: _*)
a.map( x => (x, bs.to(x).lastOption.getOrElse(Int.MinValue)) ).toMap
// res1: scala.collection.immutable.Map[Int,Int] = Map(
// 5 -> 5, 1 -> 1, 6 -> 5, 9 -> 5, 2 -> 1, 7 -> 5, 3 -> 1, 8 -> 5, 4 -> 1
// )
Note that neither list a or b needs to be ordered.
UPDATE:
Starting Scala 2.13, methods to for TreeSet is replaced with rangeTo.
Here is another approach using collect function
val a = List(1,2,3,4,5,6,7,8,9)
val b = List(1,5,10)
val result = a.collect{
case e if(b.filter(_<=e).size>0) => e -> b.filter(_<=e).reverse.head
}
//result: List[(Int, Int)] = List((1,1), (2,1), (3,1), (4,1), (5,5), (6,5), (7,5), (8,5), (9,5))
Here for every element in a check if there is a number in b i.e. which is greater than or equal to it and reverse the filter list and get its head to make it a pair.
Being new to spark and scala. I need to check how I can achieve this:
input:val x = sc.parallelize(1 to 10, 3)
o/p after collecting:
Array[Int] = Array(1,2,3,4,5))
Array[Int] = Array(2,4,6,8,10)
I guess this is what you are looking for
val evens = x.filter(value => value % 2 == 0)
val odds = x.filter(value => value % 2 != 0)
Thanks
Outputs :
scala> evens.foreach(println)
4
6
2
8
10
scala> odds.foreach(println)
5
1
3
7
9
I think this helps you to understand as per your question.
val spark =
SparkSession.builder().master("local").appName("test").getOrCreate()
import spark.implicits._
val data = spark.sparkContext.parallelize(1 to 10, 3)
data.filter(_ < 6).collect().foreach(println)
Output
1
2
3
4
5
data.filter(_%2 == 0).collect().foreach(println)
Output
2
4
6
8
10
Actually this works
object Matrixmul extends App {
val a = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8, 9))
val b = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8, 9))
val c = Array.ofDim[Int](3, 3)
val sum =Array.ofDim[Int](3,3)
println(a.mkString(" "))
val elements = for {
row <- a
ele <- row
}yield ele
for(array1 <-elements)
println(" the 1st matrix array elements are : " + array1)
This prints the arrray in the format,
the 1st matrix array elements are : 1
the 1st matrix array elements are : 2
the 1st matrix array elements are : 3
the 1st matrix array elements are : 4
the 1st matrix array elements are : 5
the 1st matrix array elements are : 6
the 1st matrix array elements are : 7
the 1st matrix array elements are : 8
the 1st matrix array elements are : 9
But I need in DIMENSION format,
1 2 3
4 5 6
7 8 9
How about the following,
val a = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8, 9))
a.foreach(row => println(row.mkString(" ")))
Which will print your dimentional format,
1 2 3
4 5 6
7 8 9
Small variation on the subject
val a = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8, 9))
println(a.map(_.mkString(" ")).mkString("\n"))
I am working on a Scala exercise which asks me to create a 2D array of 4 rows and 5 columns and store the row index+column index+5 in each element. Also I have to sum the array by rows and then by columns and print the rows total and the columns total.I am so confused and I only know how to create an empty array.
val matrix = Array.ofDim[Int](4, 5)
Can you teach me how to do the rest of this exercise?
I will not tell you "the rest of the exercise" but I will try to show one way to create a 2D collection, like an array in this case:
val matrix1D = for {
rowIndex <- (0 until 4).toArray
colIndex <- (0 until 5).toArray
} yield rowIndex + colIndex + 5
Where
scala> :t matrix1D
Array[Int]
Now the result of this for-comprehension is the 1D version of your 2D array.
EDIT
I could probably give you few more hints:
scala> (0 to 11).toArray.grouped(4).toArray
res10: Array[Array[Int]] = Array(Array(0, 1, 2, 3), Array(4, 5, 6, 7), Array(8, 9, 10, 11))
scala> .transpose
res11: Array[Array[Int]] = Array(Array(0, 4, 8), Array(1, 5, 9), Array(2, 6, 10), Array(3, 7, 11))
EDIT
After you create matrix2D from matrix1D:
val matrix2D = matrix1D.??????????????????
Where
scala> :t matrix2D
Array[Array[Int]]
To print it out, you could simply use mkString:
scala> matrix2D.map(_.mkString("\t")).mkString("\n")
res32: String =
5 6 7 8 9
6 7 8 9 10
7 8 9 10 11
8 9 10 11 12
I have some experience with R language and now I wanted to try Scala language. In R language I can assign one value to many elements of a vector, e.g.
(xs <- 1:10)
#[1] 1 2 3 4 5 6 7 8 9 10
k <- 3
xs[1:k] <- xs[k+1]
xs
# 4 4 4 4 5 6 7 8 9 10
It assigns value of k+1 element to all elements of indices from 1 to k. Is it also possible to do it without a loop in Scala (I mean Array in Scale)? I know there is slice method, but it only returns values of an Array, one cannot modify elements of the Array using this method.
What is even more, should I use Array or ArrayBuffer if I only want to change values of elements and I do not want to add/remove elements from a collection?
Check out the java.util.Arrays.fill methods.
scala> val xs = (1 to 9).toArray
xs: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9)
scala> val k = 6
k: Int = 6
scala> java.util.Arrays.fill(xs, 0, k, xs(k))
scala> xs
res10: Array[Int] = Array(7, 7, 7, 7, 7, 7, 7, 8, 9)
For your second question, if not resizing the collection but editing the elements, stick with array. ArrayBuffer is much like the Java ArrayList, it resizes it self when it needs to, so insertion is amortized constant, not just constant.
For your first question, I'm not aware of any method in the collections library that would allow you to do this. It's obviously syntactic sugar for looping, so if you really care (do you really find yourself needing to do this often?), you can define an implicit class and yourself define a method which loops, and then use that. Write a comment if you would like to see example of such code, otherwise try doing it yourself, it's gonna be good training.
Scala has the Range class. You can convert the Range to an Array if you wish.
scala> val n = 10
n: Int = 10
scala> Range(1,n)
res22: scala.collection.immutable.Range = Range(1, 2, 3, 4, 5, 6, 7, 8, 9)
scala> res22.toArray
res23: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9)
│
ArrrayBuffer has constant time update and would be good for updating values.