Compare/Intersection 列表列表

Question

我想用 intersection 查看两个列表的交集。

同时

(intersection (list 1 1) (list 1 1))

工作得很好并且 returns (1 1),

 (intersection (list (list 1 2) (list 1 4)) (list (list 1 2) (list 1 5)))

没有 return 我 (1 2) 但 NIL。

我的错误在哪里？

Answer 1

intersection takes an optional :test keyword argument to specify what definition of "equality" to use. The default is eql, which compares lists for pointer equality. Since your two lists are actually distinct lists in memory, they're not eql. Use equal 比较列表 element-wise。

  (intersection (list (list 1 2) (list 1 4)) (list (list 1 2) (list 1 5)) :test #'equal)

Compare/Intersection 列表列表

Compare/Intersection List of Lists

common-lisp