How to do multiple arguments to map function where one remains the same in python

Question

Let s say we have a function add as follows def add x  y       return x   y  we want to apply map function for an array map add   1  2  3   2   The semantics are I want to add 2 to every element of the array  But the map function requires a list in the third argument as well  Note  I am putting the add example for simplicity  My original function is much more complicated  And of course option of setting the default value of y in add function is out of question as it will be changed for every call

User · Answer

Sometimes I resolved similar situations (such as using pandas.apply method) using closures

In order to use them, you define a function which dynamically defines and returns a wrapper for your function, effectively making one of the parameters a constant.

Something like this:

def add(x, y):
   return x + y

def add_constant(y):
    def f(x):
        return add(x, y)
    return f

Then, add_constant(y) returns a function which can be used to add y to any given value:

>>> add_constant(2)(3)
5

Which allows you to use it in any situation where parameters are given one at a time:

>>> map(add_constant(2), [1,2,3])
[3, 4, 5]

edit

If you do not want to have to write the closure function somewhere else, you always have the possibility to build it on the fly using a lambda function:

>>> map(lambda x: add(x, 2), [1, 2, 3])
[3, 4, 5]

User · Answer

Map can contain multiple arguments  the standard way is   map add  a  b    In your question  it should be   map add  a   2  len a

User · Answer

Another option is   results      for x in  1 2 3       z   add x 2              results     f z x y     This format is very useful when calling multiple functions

User · Answer

I believe starmap is what you need   from itertools import starmap   def test x  y  z       return x   y   z  list starmap test    1  2  3    4  5  6

User · Answer

You can include lambda along with map   list map lambda a  a 2   1  2  3

User · Answer

One option is a list comprehension    add x  2  for x in  1  2  3     More options   a    1  2  3   import functools map functools partial add  y 2   a   import itertools map add  a  itertools repeat 2  len a

User · Answer

If you have it available  I would consider using numpy  It s very fast for these types of operations    gt  gt  gt  import numpy  gt  gt  gt  numpy array  1 2 3     2 array  3  4  5     This is assuming your real application is doing mathematical operations  that can be vectorized

User · Answer

The correct answer is simpler than you think  Simply do   map add    x  2  for x in  1 2 3      And change the implementation of add to take a tuple i e  def add t      x  y   t    return x y   This can handle any complicated use case where both add parameters are dynamic

User · Answer

Use a list comprehension    x   2 for x in  1  2  3     If you really  really  really want to use map  give it an anonymous function as the first argument   map lambda x  x   2   1 2 3

User · Answer

The docs explicitly suggest this is the main use for itertools repeat      Make an iterator that returns object over and over again  Runs indefinitely unless the times argument is specified  Used as argument to map   for invariant parameters to the called function  Also used with zip   to create an invariant part of a tuple record     And there s no reason for pass len  1 2 3   as the times argument  map stops as soon as the first iterable is consumed  so an infinite iterable is perfectly fine    gt  gt  gt  from operator import add  gt  gt  gt  from itertools import repeat  gt  gt  gt  list map add   1 2 3   repeat 4     5  6  7    In fact  this is equivalent to the example for repeat in the docs    gt  gt  gt  list map pow  range 10   repeat 2     0  1  4  9  16  25  36  49  64  81    This makes for a nice lazy-functional-language-y solution that s also perfectly readable in Python-iterator terms

User · Answer

To pass multiple arguments to a map function   def q x y       return x y  print map  q range 0 10  range 10 20     Here q is function with multiple argument that map   calls  Make sure  the length of both the ranges i e   len  range a a    and len  range b b    are equal

User · Answer

multi argument  def joke r        if len r   2            x  y   r           return x   y      elif len r   3             x y z r            return x y z   using map      print list map joke   2 3   3 4 5       output    6 12  if the case like above and just want use function def add x y       ar         for xx in x           ar append xx y      return ar print list map add   3 2 4    2    0   output    5 4 6   Note  you can modified as you want

User · Answer

If you really really need to use map function  like my class assignment here      you could use a wrapper function with 1 argument  passing the rest to the original one in its body  i e     extraArguments   value def myFunc arg         call the target function     return Func arg  extraArguments    map myFunc  itterable    Dirty  amp  ugly  still does the trick

User · Answer

def func a  b  c  d    return a   b   c   d   map lambda x  func  x     1 2 3 4    5 6 7 8       By wrapping the function call with a lambda and using the star unpack  you can do map with arbitrary number of arguments

User · Answer

In  nums    1  2  3   In  map add  nums   2  len nums    Out  3  4  5

[python] How to do multiple arguments to map function where one remains the same in python?

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