Does python have an equivalent to C#'s Enumerable.Aggregate?

Question

In C#, if I have a collection of strings, and I want to get a comma-separated string representing of the collection (without extraneous comments at the beginning or end), I can do this:

string result = collection.Aggregate((s1, s2) => String.Format("{0}, {1}", s1, s2));

I could do something like

result = collection[0]
for string in collection[1:]:
    result = "{0}, {1}".format(result, string)

But this feels like a cludge. Does python have an elegant way to accomplish the same thing?

Answer 1

Use str.join :

result = ', '.join(iterable)

If not all the items in the collection are strings, you can use map or a generator expression:

result = ', '.join(str(item) for item in iterable)

Answer 2

The Equivalent of the C# Enumerable.Aggregate method is pythons built in "reduce" method. For example,

reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) 

Calculates ((((1+2)+3)+4)+5). which is 15

This means you could achieve the same with

result = reduce(lambda s1, s2: "{0}, {1}".format(s1, s2), collection)

Or with

result = reduce(lambda s1, s2: s1 + ", " + s2, collection)

In your Case it would be better to use ', '.join as others have suggested because of pythons immutable strings.

For completeness the C# Enumerable.Select method in python is "map".

Now if anyone asks you can say you know MapReduce :)

Answer 3

You could do something like:

> l = [ 1, 3, 5, 7]
> s = ", ".join( [ str(i) for i in l ] )
> print s
1, 3, 5, 7

I suggest looking up "python list comprehensions" (the [ ... for ... ] in the above) for more info.