CODEWITHSUNDEEP
pythonlambda
disruptive
disruptive

Reputation: 5946

Complex expressions in python reduce

Is there a smart way to sum a list, but actually perform a map type function prior to summing.

I'm trying to combine these functions into one function that uses the lambda:

xlist = [1, 2, 3, 4]
sum(map(lambda x: (x - 1.0)**2, xlist))

# result = 14.0

I'm trying this:

reduce(lambda x, y: x + (y - 1.0)**2, xlist)

# result = 15.0

But it is not the same result. What is the smartest way to solve this. I'm kind of curious, I know I can use sum(map()) but I wonder if reduce can be used in this way.

Upvotes: 1

Views: 417

Answers (1)

user2555451
user2555451

Reputation:

Yea, you just need to pass an initial value of 0:

>>> xlist = [1, 2, 3, 4]
>>> reduce(lambda x, y: x + (y - 1.0)**2, xlist, 0)
14.0
>>>

Keep in mind though that reduce is generally hated by Python programmers because of how unreadable it is. You would probably be better off using the first approach.

Or, even better, use a generator expression:

sum((x - 1.0)**2 for x in xlist)

This is a lot easier to read and is also more efficient because map creates an unnecessary list.

Upvotes: 7

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