Use of Map

Map is a very useful feature, let's give a simple example

Operation of two list elements

(Map + ' (1 2 3) ' (  ) → (51 62 73)

If action for two list elements

(Map if ' (True nil true nil True) ' (1 2 3 4 5) ' (6 7 8 9 10) → ' (1 7 3 9 5)

This is a bit of a meaning, rather with a bunch of bool values to determine whether to pick elements from the first list, or to pick from the second list. Then make a new list.

Use a lambda expression for two lists

(Map (FN (x y) (* x y)) ' (3 4) ' (20 10) → (60 40)

Extract all data from a column in a two-dimensional table

This syntax is very practical and now shows the Rickybody code in the community:

(New Class ' Node) (Set ' l ' (List (node "A" ' Happy) (node "B" ' Sad ") (node" C "' Happy") (node "      D" ' indifferent) (node "      E" ' Surly (      node "F" ' Happy) (      node "G" ' Sad) ") (println (Map (FN (n) (n 0) L))

The output is:

(Node node node, node node)

if (n 0) is changed to (n 1), the result is:

("A" "B" "C" "D" "E" "F" "G")

Explain:

This creates a node class that uses the newLISP foop mode. Then put multiple node objects in a list, such as Foop, each object is a list, the first element is a type, the second element is the object name, and the third element is an attribute. It looks like a two-dimensional table with three columns and seven rows.

This custom function (FN (n) (n 0)) extracts the No. 0 element in the list of objects and, of course, extracts the 1th and 2nd.

The result becomes a list.

Use of Map