Clean code for sequence of map/filter/reduce functions

Question

Is there a simple way to code in one line a sequence of map/filter/reduce functions?

For example instead of:

reduce(lambda x, y: x*y, filter(lambda x: x>0, map(lambda x: x - 1, some_list)))

I am looking for something like:

some_list.map(lambda x: x -1, a).filter(lambda x: x>0).reduce(lambda x, y: x*y)

Answer 1

PyFunctional lets you do exactly that after installing via pip install PyFunctional

from functional import seq  seq(some_list).map(lambda x: x -1, a).filter(lambda x: x>0).reduce(lambda x, y: x*y) 

The package can do much more than that, which you can checkout at github.com/EntilZha/PyFunctional

Answer 2

If you can use foreign library, look for

https://github.com/serkanyersen/underscore.py

It is python port of underscore.js. Therefore you can use chain() method to begin filter, map, reduce , and get the result by value() method.

Using this library, you can write something like

from underscore import _
my_array = [10, 48, -1, 30, 20, 0]
result = _(my_array).chain().map(lambda x,*a: x - 1).filter(lambda x: x > 0).reduce(lambda x,y,*a: x*y, 1).value()

I tested in python 3.4.2 and seems to work fine.

Answer 3

You can use your own list:

class Mylist(list):

    def __init__(self, l):
        list.__init__(self,l)

    def map(self, f):
        return Mylist(map(f, self[:]))

In this case, we just subclass the list to a new list method. Then, you can add the map, filter and reduce methods to the class. I have shown how to add the map method. The other functions will be very similar.

Note that in this case, you can chain the map and filter functions as much as you want, but the reduce method will generally not result in a list it wont be possible to chain functions anymore.

Here is an example output:

In [16]: xx = Mylist([1,2,3])

In [17]: xx.map(lambda m: m*2).map(lambda m: m**2)
Out[17]: [4, 16, 36]