时间戳

首页 > 解决方案 > 如何从流氓地图中获取所有键？

rascal - 如何从流氓地图中获取所有键？

问题描述

假设我有一张这样的地图：

map[str,int] a = ("apple": 1, "pear": 2, "banana": 3, "kiwi": 4);

有没有办法返回地图中的所有键，即“apple”、“pear”、“banana”、“kiwi”？从http://tutor.rascal-mpl.org/Rascal/Expressions/Values/Map/Comprehension/Comprehension.html#/Rascal/Expressions/Values/Map/Map.html的文档来看，似乎没有内置的方式。可能吗？

标签： rascal

解决方案

多种方式：

首先只是突出第一列：

rascal>map[str,int] a = ("apple": 1, "pear": 2, "banana": 3, "kiwi": 4); 
map[str, int]: ("banana":3,"pear":2,"kiwi":4,"apple":1)
rascal>a<0>
set[str]: {"banana","pear","kiwi","apple"}

其次是标记列，并做同样的事情（<>符号或.符号）

rascal>map[str fruit, int count] b = ("apple": 1, "pear": 2, "banana": 3, "kiwi": 4); 
map[str fruit, int count]: ("banana":3,"pear":2,"kiwi":4,"apple":1)
rascal>b<fruit>
set[str]: {"banana","pear","kiwi","apple"}
rascal>b.fruit
set[str]: {"banana","pear","kiwi","apple"}

最后，地图也是它们自己的键的生成器，如下所示：

rascal>[ f | f <- a]
list[str]: ["banana","pear","kiwi","apple"]
rascal>{ f | f <- a}
set[str]: {"banana","pear","kiwi","apple"}
rascal>import IO;
rascal>for (f <- a)
>>>>>>>  println(f);
banana
pear
kiwi
apple

推荐阅读