map-function | 易学教程

Python 3 Map function is not Calling up function

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Why doesn't following code print anything: #!/usr/bin/python3 class test: def do_someting(self,value): print(value) return value def fun1(self): map(self.do_someting,range(10)) if __name__=="__main__": t = test() t.fun1() I'm executing the above code in Python 3. I think i'm missing something very basic but not able to figure it out. map() returns an iterator , and will not process elements until you ask it to. Turn it into a list to force all elements to be processed: list(map(self.do_someting,range(10))) or use collections.deque() with the length set to 0 to not produce a list if you don't

Function application over numpy's matrix row/column

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I am using Numpy to store data into matrices. Coming from R background, there has been an extremely simple way to apply a function over row/columns or both of a matrix. Is there something similar for python/numpy combination? It's not a problem to write my own little implementation but it seems to me that most of the versions I come up with will be significantly less efficient/more memory intensive than any of the existing implementation. I would like to avoid copying from the numpy matrix to a local variable etc., is that possible? The functions I am trying to implement are mainly simple

Passing multiple parameters to pool.map() function in Python [duplicate]

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This question already has an answer here: Python multiprocessing pool.map for multiple arguments 18 answers I need some way to use a function within pool.map() that accepts more than one parameter. As per my understanding, the target function of pool.map() can only have one iterable as a parameter but is there a way that I can pass other parameters in as well? In this case, I need to pass in a few configuration variables, like my Lock() and logging information to the target function. I have tried to do some research and I think that I may be able to use partial functions to get it to work?

Lazy evaluation of map

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问题 I recently read that one benefit of map in Python 3 was that it is lazy. That means, it is better to do map(lambda x: x**2, range(10**100)) rather than [x**2 for x in range(10**100)] What I'm curious about, is how I can put this laziness to use. If I generate the map object, how can I, for example, access a particular element in the resulting operation/list. In almost every documentation on map I've seen, they will do something like print(map(...)) or for i in map(...) which (as far as I

Mapping a nested list with List Comprehension in Python?

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问题 I have the following code which I use to map a nested list in Python to produce a list with the same structure. >>> nested_list = [['Hello', 'World'], ['Goodbye', 'World']] >>> [map(str.upper, x) for x in nested_list] [['HELLO', 'WORLD'], ['GOODBYE', 'WORLD']] Can this be done with list comprehension alone (without using the map function)? 回答1: For nested lists you can use nested list comprehensions: nested_list = [[s.upper() for s in xs] for xs in nested_list] Personally I find map to be

Using Array.map with new Array constructor

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问题 I was trying to use new Array() constructor with map in order to create a one-line code that creates a list of elements. Something like this : let arr = new Array(12).map( (el, i) => { console.log('This is never called'); return i + 1; }); Reading docs, the behaviour makes sense. Basically docs say that callback of map will be executed even for declared undefined values in array, but not for example when creating empty Arrays like the code before. So this should work : var arr = new Array(12)

Using map() function with keyword arguments

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Here is the loop I am trying to use the map function on: volume_ids = [1,2,3,4,5] ip = '172.12.13.122' for volume_id in volume_ids: my_function(volume_id, ip=ip) Is there a way I can do this? It would be trivial if it weren't for the ip parameter, but I'm not sure how to deal with that. Use functools.partial() : from functools import partial mapfunc = partial(my_function, ip=ip) map(mapfunc, volume_ids) partial() creates a new callable, that'll apply any arguments (including keyword arguments) to the wrapped function in addition to whatever is being passed to that new callable. Here is a

Map function in MATLAB?

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I'm a little surprised that MATLAB doesn't have a Map function, so I hacked one together myself since it's something I can't live without. Is there a better version out there? Is there a somewhat-standard functional programming library for MATLAB out there that I'm missing? function results = map(f,list) % why doesn't MATLAB have a Map function? results = zeros(1,length(list)); for k = 1:length(list) results(1,k) = f(list(k)); end end usage would be e.g. map( @(x)x^2,1:10) The short answer: the built-in function arrayfun does exactly what your map function does for numeric arrays: >> y =

Mapping over values in a python dictionary

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Given a dictionary { k1: v1, k2: v2 ... } I want to get { k1: f(v1), k2: f(v2) ... } provided I pass a function f . Is there any such built in function? Or do I have to do dict([(k, f(v)) for (k, v) in my_dictionary.iteritems()]) Ideally I would just write my_dictionary.map_values(f) or my_dictionary.mutate_values_with(f) That is, it doesn't matter to me if the original dictionary is mutated or a copy is created. There is no such function; the easiest way to do this is to use a dict comprehension: my_dictionary = {k: f(v) for k, v in my_dictionary.items()} In python 2.7, use the .iteritems()

Mapping a function on the values of a map in Clojure

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I want to transform one map of values to another map with the same keys but with a function applied to the values. I would think there was a function for doing this in the clojure api, but I have been unable to find it. Here's an example implementation of what I'm looking for (defn map-function-on-map-vals [m f] (reduce (fn [altered-map [k v]] (assoc altered-map k (f v))) {} m)) (println (map-function-on-map-vals {:a "test" :b "testing"} #(.toUpperCase %))) {:b TESTING, :a TEST} Does anybody know if map-function-on-map-vals already exists? I would think it did (probably with a nicer name too).