reduce

I'm new to Python. Would you please tell me what's wrong with the following code? When I run it, I got an error message of "NameError: global name 'reduce' is not defined". I asked Goolge but it's useless. :( def main(): def add(x,y): return x+y reduce(add, range(1, 11)) if __name__=='__main__': main() I'm going to guess that: You are using Python 3, and You are following a tutorial designed for Python 2. The reduce function, since it is not commonly used, was removed from the built-in functions in Python 3. It is still available in the functools module, so you can do: import functools def

When doing a "join" in CouchDB, you can use view collation to group the records together. For example, having two document types customers and orders . So that you can return customer , then all the orders for that customer, then the next customer, and orders. The question is, how do you do a merging of rows, so that if you have 10 customers, and 40 orders, your output is still 10 rows instead of 50. You essentially add more information into your customer row. I believe using a _list or a reduce will solve this. The question is how exactly to do this? Marcello Nuccio I second jhs answer , but

I saw that they were documented together here . Are they the same thing? Why does Ruby have so many aliases (such as map/collect for arrays)? Thanks a lot. Yes, and it's also called fold in many other programming languages and in Mathematics. Ruby aliases a lot in order to be intuitive to programmers with different backgrounds. If you want to use #length on an Array , you can. If you want to use #size , that's fine too! More recent versions of the documentation of Enumerable#reduce specify it explicitly: The inject and reduce methods are aliases. There is no performance benefit to either. 来源：

Lets say you have two document types, customers and orders . A customer document contains basic information like name, address etc. and orders contain all the order information each time a customer orders something. When storing the documents, the type = order or the type = customer. If I do a map function over a set of 10 customers and 30 orders it will output 40 rows. Some rows will be customers, some will be orders. The question is, how do I write the reduce, so that the order information is "stuffed" inside of the rows that has the customer information? So it will return 10 rows (10

Trying to learn F# but got confused when trying to distinguish between fold and reduce . Fold seems to do the same thing but takes an extra parameter. Is there a legitimate reason for these two functions to exist or they are there to accommodate people with different backgrounds? (E.g.: String and string in C#) Here is code snippet copied from sample: let sumAList list = List.reduce (fun acc elem -> acc + elem) list let sumAFoldingList list = List.fold (fun acc elem -> acc + elem) 0 list printfn "Are these two the same? %A " (sumAList [2; 4; 10] = sumAFoldingList [2; 4; 10]) Fold takes an