![]() Note: At minimum map() needs two arguments. If you want to increment every number in the list, you can do the following: > map(add_one, my_list) You also have a list of numbers: my_list = Imagine you have a function that takes a number, adds 1 to that number and returns it: def add_one(num): Map() can iterate over every item in a list and apply a function to each item, than it will return (give you back) the new list. The map() function is there to apply the same procedure to every item in an iterable data structure, like lists, generators, strings, and other stuff. But to tell the truth, using product() is a much simpler and natural way to solve the problem: from itertools import productĮither way, the result is the cartesian product of lst as defined above: [(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), Reduce(add, map(lambda i: map(lambda j: (i, j), lst), lst)) If one iterable is shorter than another it is assumed to be extended with None items.įor the second part in the question: What role does this play in making a Cartesian product? well, map() could be used for generating the cartesian product of a list like this: lst = If additional iterable arguments are passed, function must take that many arguments and is applied to the items from all iterables in parallel. I said "simplifying a bit" because in reality map() can process more than one iterable: Simplifying a bit, you can imagine map() doing something like this: def mymap(func, lst):Īs you can see, it takes a function and a list, and returns a new list with the result of applying the function to each of the elements in the input list. But also note again that a list comprehension is usually preferred: > Note that map(list, a) is equivalent in Python 2, but in Python 3 you need the list call if you want to do anything other than feed it into a for loop (or a processing function such as sum that only needs an iterable, and not a sequence). ('h', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd')Ī use of map here would be if you start with a list of strings instead of a single string - map can listify all of them individually: > a = ![]() Map in Python 3 is equivalent to this: def map(func, iterable):Īnd the only difference in Python 2 is that it will build up a full list of results to return all at once instead of yielding.Īlthough Python convention usually prefers list comprehensions (or generator expressions) to achieve the same result as a call to map, particularly if you're using a lambda expression as the first argument: Īs an example of what you asked for in the comments on the question - "turn a string into an array", by 'array' you probably want either a tuple or a list (both of them behave a little like arrays from other languages) - > a = "hello, world" Map doesn't relate to a Cartesian product at all, although I imagine someone well versed in functional programming could come up with some impossible to understand way of generating a one using map. The reference definitions is also hard to understand. I want to fully understand this function. What effect does putting a tuple anywhere in there have? I also noticed that without the map function the output is abc and with it, it's a, b, c. What role does this play in making a Cartesian product? content = map(tuple, array) The iterable arguments may be a sequence or any iterable object the Multiple arguments, map() returns a list consisting of tuplesĬontaining the corresponding items from all iterables (a kind of If function is None, the identity function is assumed if there are If one iterable is shorter than another it is assumed to be extended Take that many arguments and is applied to the items from all If additional iterable arguments are passed, function must )Īpply function to every item of iterable and return a list of the ![]() The Python 2 documentation says: Built-in Functions: map(function, iterable.
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