scala中map添加值

A Map is a data structure that stores data as key: value pair.

映射是一種將數(shù)據(jù)存儲(chǔ)為鍵：值對的數(shù)據(jù)結(jié)構(gòu)。

Syntax:

句法：

Map(key->value, key->value)

反轉(zhuǎn)地圖中的鍵和值 (Reversing Keys and values in Map)

Here, we will see a program to reverse keys and values in Scala Map. We will reverse the values to keys and the keys to pairs.

在這里，我們將看到一個(gè)在Scala Map中反轉(zhuǎn)鍵和值的程序 。 我們將值反轉(zhuǎn)為鍵，將鍵反轉(zhuǎn)為對。

So, before this, we will have to make sure that both keys and values of the initial map are unique to avoid errors.

因此，在此之前，我們必須確保初始映射的鍵和值都唯一以避免錯(cuò)誤。

Program:

程序：

object myObject { def main(args:Array[String]) { val bikes = Map(1->"S1000RR" , 2->"R1", 3->"F4" ) println("Inital map: " + bikes) val reverse = for ((a, b) <- bikes) yield (b, a) println("Reversed map: " + reverse) } }

Output

輸出量

Inital map: Map(1 -> S1000RR, 2 -> R1, 3 -> F4) Reversed map: Map(S1000RR -> 1, R1 -> 2, F4 -> 3)

Explanation:

說明：

Here, we have declared a map and then reversed its values. In the reverse variable, we have inserted value that is reverse of each pair of the original map, the yield methods take the (key, value) pair and returns (value, key) pair to the reverse map.

在這里，我們聲明了一個(gè)映射，然后反轉(zhuǎn)了它的值。 在反向變量中，我們插入了與原始映射的每對相反的值，yield方法采用( key，value )對，然后將( value，key )對返回到反向映射。

What if values are not unique?

如果值不是唯一的怎么辦？

There is a thing that is needed to be considered is both key-value pairs should be unique. But if we insert a duplicate in value, in the reverse map this will delete that pair.

有一點(diǎn)需要考慮的是，兩個(gè)鍵值對都應(yīng)該是唯一的。 但是，如果我們在值中插入重復(fù)項(xiàng)，則在反向映射中將刪除該對。

Program:

程序：

object myObject { def main(args:Array[String]) { val bikes = Map(1->"S1000RR" , 2->"R1", 3->"F4", 4->"S1000RR" ) println("Inital map: " + bikes) val reverse = for ((a, b) <- bikes) yield (b, a) println("Reversed map: " + reverse) } }

Output

輸出量

Inital map: Map(1 -> S1000RR, 2 -> R1, 3 -> F4, 4 -> S1000RR) Reversed map: Map(S1000RR -> 4, R1 -> 2, F4 -> 3)

So, the code runs properly but the reverse will delete the pair 4->S100RR to make all the keys of reverse map unique.

因此，代碼可以正常運(yùn)行，但是反向鍵將刪除對4-> S100RR以使反向鍵的所有鍵都唯一。

翻譯自: https://www.includehelp.com/scala/reverse-keys-and-values-in-scala-map.aspx

scala中map添加值

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