A In Scala language In the above grammar The following is an example that uses the The output result of executing the above code is: The following is an example that uses the The output result of executing the above code is: In The output result of executing the above code is: The In the above grammar The following example loops a collection of numbers. We use The output result of executing the above code is: Scala can use one or more The following is in You can use the semicolon (;) to add one or more filter criteria to the expression. The following is The output result of executing the above code is: You can put Note that curly braces are used to hold variables and conditions The following example demonstrates The output result of executing the above code is:
In recent years, Geographic Information Systems (GIS) have undergone rapid development in both theoretical and practical dimensions. GIS has been widely applied for modeling and decision-making support across various fields such as urban management, regional planning, and environmental remediation, establishing geographic information as a vital component of the information era. The introduction of the “Digital Earth” concept has further accelerated the advancement of GIS, which serves as its technical foundation. Concurrently, scholars have been dedicated to theoretical research in areas like spatial cognition, spatial data uncertainty, and the formalization of spatial relationships. This reflects the dual nature of GIS as both an applied technology and an academic discipline, with the two aspects forming a mutually reinforcing cycle of progress. for loop allows you to write a loop control structure that executes a specified number of times. 8.13.1. Grammar #
for the syntax of the loop:for( var x <- < span> Range ){
statement(s);
}
Range can be a number interval representation. i to j , or i until j . The left arrow <-is < assign p thevariable to used values x.> 8.13.2. Example #
i to j an example of the syntax (including j): Example #
object Test {
def main(args: Array[String]) {
var a = 0;
// for loop
for( a <- < span> 1 to 10){
println( "Value of a: " + a );
}
}
}
$ scalac Test.scala
$ scala Test
value of a: 1
value of a: 2
value of a: 3
value of a: 4
value of a: 5
value of a: 6
value of a: 7
value of a: 8
value of a: 9
value of a: 10
i until j an example of the syntax (excluding j): Example #
object Test {
def main(args: Array[String]) {
var a = 0;
// for loop
for( a <- < span> 1 until 10){
println( "Value of a: " + a );
}
}
}
$ scalac Test.scala
$ scala Test
value of a: 1
value of a: 2
value of a: 3
value of a: 4
value of a: 5
value of a: 6
value of a: 7
value of a: 8
value of a: 9
for the loop you can use the semicolon (;) to set multiple intervals, which will iterate over all possible values for a given interval.The following example shows an example of a loop in two intervals: Example #
object Test {
def main(args: Array[String]) {
var a = 0;
var b = 0;
// for loop
for( a <- < span> 1 to 3; b <- < span> 1 to 3){
println( "Value of a: " + a );
println( "Value of b: " + b );
}
}
}
$ scalac Test.scala
$ scala Test
Value of a: 1
Value of b: 1
Value of a: 1
Value of b: 2
Value of a: 1
Value of b: 3
Value of a: 2
Value of b: 1
Value of a: 2
Value of b: 2
Value of a: 2
Value of b: 3
Value of a: 3
Value of b: 1
Value of a: 3
Value of b: 2
Value of a: 3
Value of b: 3
8.13.3.
for Cyclic set # for syntax for a loop collection is as follows: for( x <- < span> List ){
statement(s);
}
List a variable is a collection, and the for loop iterates over the elements of all collections. 8.13.4. Example #
List() to create a collection. We will describe the collection in detail in later chapters. Example #
object Test {
def main(args: Array[String]) {
var a = 0;
val numList = List(1,2,3,4,5,6);
// for loop
for( a <- < span> numList ){
println( "Value of a: " + a );
}
}
}
$ scalac Test.scala
$ scala Test
value of a: 1
value of a: 2
value of a: 3
value of a: 4
value of a: 5
value of a: 6
8.13.5.
for Cyclic filtration # if statement to filter some elements. for the syntax for using filters in a loop. for( var x <- < span> List
if condition1; if condition2...
){
statement(s);
}
8.13.6. Example #
for instances filtered in the loop: Example #
object Test {
def main(args: Array[String]) {
var a = 0;
val numList = List(1,2,3,4,5,6,7,8,9,10);
// for loop
for( a <- < span> numList
if a != 3; if a < 8 ){
println( "Value of a: " + a );
}
}
}
$ scalac Test.scala
$ scala Test
value of a: 1
value of a: 2
value of a: 4
value of a: 5
value of a: 6
value of a: 7
8.13.7. For uses yield #
for the return value of the loop is stored as a variable. The syntax format is as follows: var retVal = for{ var x <- < span> List
if condition1; if condition2...
}yield x
retVal ,it’s a variable, in a loop. yield the current element is written down and saved in the collection, which is returned at the end of the loop. 8.13.8. Example #
for use in a loop yield : Example #
object Test {
def main(args: Array[String]) {
var a = 0;
val numList = List(1,2,3,4,5,6,7,8,9,10);
// for loop
var retVal = for{ a <- < span> numList
if a != 3; if a < 8
}yield a
// Output return value
for( a <- < span> retVal){
println( "Value of a: " + a );
}
}
}
$ scalac Test.scala
$ scala Test
value of a: 1
value of a: 2
value of a: 4
value of a: 5
value of a: 6
value of a: 7
Principles, Technologies, and Methods of Geographic Information Systems
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