通常，REDUCE，FOLD，SCAN方法通过在LEFT上累积数据并继续更改RIGHT变量而起作用。它们之间的主要区别是REDUCE，FOLD是：
折叠始终以一个seed值开始，即用户定义的起始值。如果collection为空，并且fold会返回种子值，那么Reduce会抛出异常。将始终产生单个值。
扫描用于从左侧或右侧对项目的某些处理顺序，然后我们可以在后续计算中利用先前的结果。这意味着我们可以扫描物品。总是会产生一个集合。
以下代码的部分输出将是：-
scan对数字列表使用操作（使用seed值0）List(-2,-1,0,1,2)
{0，-2} =>-2 {-2，-1} =>-3 {-3,0} =>-3 {-3,1} =>-2 {-2,2} => 0扫描列表（0，-2，-3，-3，-2，0）
{0，-2} =>-2 {-2，-1} =>-3 {-3,0} =>-3 {-3,1} =>-2 {-2,2} => 0 scanLeft（a + b）列表（0，-2，-3，-3，-2，0）
{0，-2} =>-2 {-2，-1} =>-3 {-3,0} =>-3 {-3,1} =>-2 {-2,2} => 0 scanLeft（b + a）列表（0，-2，-3，-3，-2，0）
{2,0} => 2 {1,2} => 3 {0,3} => 3 {-1,3} => 2 {-2,2} => 0 scanRight（a + b）列表（ 0、2、3、3、2、0）
{2,0} => 2 {1,2} => 3 {0,3} => 3 {-1,3} => 2 {-2,2} => 0 scanRight（b + a）列表（ 0、2、3、3、2、0）
使用reduce，fold对字符串列表进行操作List("A","B","C","D","E")
- {A，B} => AB {AB，C} => ABC {ABC，D} => ABCD {ABCD，E} => ABCDE降低（a + b）ABCDE
- {A，B} => AB {AB，C} => ABC {ABC，D} => ABCD {ABCD，E} => ABCDE reduceLeft（a + b）ABCDE
- {A，B} => BA {BA，C} => CBA {CBA，D} => DCBA {DCBA，E} => EDCBA reduceLeft（b + a）EDCB
- {D，E} => DE {C，DE} => CDE {B，CDE} => BCDE {A，BCDE} => ABCDE reduceRight（a + b）ABCDE
- {D，E} => ED {C，ED} => EDC {B，EDC} => EDCB {A，EDCB} => EDCBA reduceRight（b + a）EDCBA
代码：
object ScanFoldReduce extends App {
val list = List("A","B","C","D","E")
println("reduce (a+b) "+list.reduce((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" ")
a+b
}))
println("reduceLeft (a+b) "+list.reduceLeft((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" ")
a+b
}))
println("reduceLeft (b+a) "+list.reduceLeft((a,b)=>{
print("{"+a+","+b+"}=>"+ (b+a)+" " )
b+a
}))
println("reduceRight (a+b) "+list.reduceRight((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
a+b
}))
println("reduceRight (b+a) "+list.reduceRight((a,b)=>{
print("{"+a+","+b+"}=>"+ (b+a)+" ")
b+a
}))
println("scan "+list.scan("[")((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
a+b
}))
println("scanLeft (a+b) "+list.scanLeft("[")((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
a+b
}))
println("scanLeft (b+a) "+list.scanLeft("[")((a,b)=>{
print("{"+a+","+b+"}=>"+ (b+a)+" " )
b+a
}))
println("scanRight (a+b) "+list.scanRight("[")((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
a+b
}))
println("scanRight (b+a) "+list.scanRight("[")((a,b)=>{
print("{"+a+","+b+"}=>"+ (b+a)+" " )
b+a
}))
//Using numbers
val list1 = List(-2,-1,0,1,2)
println("reduce (a+b) "+list1.reduce((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" ")
a+b
}))
println("reduceLeft (a+b) "+list1.reduceLeft((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" ")
a+b
}))
println("reduceLeft (b+a) "+list1.reduceLeft((a,b)=>{
print("{"+a+","+b+"}=>"+ (b+a)+" " )
b+a
}))
println(" reduceRight (a+b) "+list1.reduceRight((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
a+b
}))
println(" reduceRight (b+a) "+list1.reduceRight((a,b)=>{
print("{"+a+","+b+"}=>"+ (b+a)+" ")
b+a
}))
println("scan "+list1.scan(0)((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
a+b
}))
println("scanLeft (a+b) "+list1.scanLeft(0)((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
a+b
}))
println("scanLeft (b+a) "+list1.scanLeft(0)((a,b)=>{
print("{"+a+","+b+"}=>"+ (b+a)+" " )
b+a
}))
println("scanRight (a+b) "+list1.scanRight(0)((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
a+b}))
println("scanRight (b+a) "+list1.scanRight(0)((a,b)=>{
print("{"+a+","+b+"}=>"+ (a+b)+" " )
b+a}))
}