Scala series: map and tuple

Map Construction Map

Immutable:

Val map = map ("sa"-> 1, "S"-> 2)
Map ("sa") = 3 // Error

Val emptymap = new scala. collection. Immutable. hashmap [String, int]

Variable:

Val MAP2 = scala. collection. mutable. Map ("sa"-> 2)
MAP2 ("sa") = 3

Val emptymap = new scala. collection. mutable. hashmap [String, int]

Note:-> used to create tuples, "sa"-> 1 ("sa", 1)

Initialization is complete with Val map = map ("sa", 1), ("S", 2 ))

Obtain the value in map:

If map does not contain the key value used in the request, an exception is thrown. Nosuchelementexception

Map ("sa") // similar to map. Get ("sa") in Java ")

To check whether a map contains a key, use the contains method.

Val SA = If (map2.contains ("sa3") MAP2 ("sa3") else 0;

Shortcut:

Val SA2 = map. getorelse ("SA2", 0)

Obtain whether the key is included at a time and obtain the value:

Val sa3 = map. Get ("sa3"); // option type,
Println (sa3.isempty)

Update values in map:

Add or update:

Map ("sa") = 3

Add or update multiple:

MAP + = ("AA"-> 4, "BB"-> 5)

Remove a key and the corresponding value:

Map-= "AA"

You can also use the + and-operations for an immutable map, but a new map is generated.

VaR map = map ("AA"-> 1)

Map = map + ("BB"-> 2)

MAP + = ("cc"-> 2)

Map-= "AA"

Iterative map:

For (K, v) <-map ){

// Todo

}

All keys:

Map. keyset

All values:

Map. Values

Reverse:

MAP2 = for (K, v) <-map) yield (v, k)

Sorted map:

Sort by key:

Sortedmap

Add order:

Linkedhashmap

Map and Java interoperability:

Convert Java properties to Scala. collection. MAP:

Import scala. collection. javaconversions. propertiesasscalamap
Val prop: scala. collection. Map [String, string] = system. getproperties ();

Convert Java map to Scala. collection. mutable. Map [String, int]:

Import scala. collection. javaconversions. mapasscalamap
Val map: scala. collection. mutable. Map [String, int] = new treemap [String, int]

Scala map to Java map:

Import scala. collection. javaconversions. mapasjavamap
Import java. AWT. Font. textattribute ._
VaR FS = map (family-> "serif", size-> 12)
VaR fonts = new font (FS)

 

Tuple:

Set of different types of Values

Val TP = (1, "SS", 2.0)

Access value:

TP. _ 1

TP. _ 2

TP. _ 3

Subscript starts from 1

Obtain the tuples through pattern matching:

Val (First, Second, Third) = Set

 

It can be used when a function returns multiple values.

Zipper operation

Val arrkey = array (1, 3, 5)
Val arrvalue = array ("A", "B", "C ")
Val tuplearr = arrkey.zip (arrvalue) // tuplearr is array (1, A), (3, B), (5, c ))
Val map = tuplearr. tomap

 

Scala series: map and tuple