问题
I would like to map three different functions, in order, over a single list. To demonstrate what I mean, say we want to do the following three mappings:
(map foo mylist)
(map bar mylist)
(map foobar mylist)
If we define mylist as '(1 2 3), and we run the above functions one at a time, we get:
(map foo mylist) ===> (foo1 foo2 foo3)
(map bar mylist) ===> (bar1 bar2 bar3)
(map foobar mylist) ===> (foobar1 foobar2 foobar3)
Instead, I would like the output to be in the following format:
===> ((foo1 bar1 foobar1) (foo2 bar2 foobar2) (foo3 bar3 foobar3))
How would you go about this?
回答1:
You can nest two maps to achieve the desired effect:
(map (lambda (e)
(map (lambda (f) (f e))
myfuncs))
mylist)
In the above mylist is the input list and myfuncs is the list of functions. For example, these lists:
(define myfuncs (list sqrt square cube))
(define mylist '(1 2 3))
... Will produce this output:
'((1 1 1) (1.4142135623730951 4 8) (1.7320508075688772 9 27))
来源：https://stackoverflow.com/questions/19145726/mapping-multiple-functions-in-order-over-a-single-list