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Python: Calculate the average of a given list, after mapping each element to a value using the provided function

Python List: Exercise - 238 with Solution

Write a Python program to calculate the average of a given list, after mapping each element to a value using the provided function.

  • Use map() to map each element to the value returned by fn.
  • Use sum() to sum all of the mapped values, divide by len(lst).
  • Omit the last argument, fn, to use the default identity function.

Sample Solution:

Python Code:

def average_by(lst, fn = lambda x: x):
  return sum(map(fn, lst), 0.0) / len(lst)

print(average_by([{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }], lambda x: x['n']))
print(average_by([{ 'n': 10 }, { 'n': 20 }, { 'n': -30 }, { 'n': 60 }], lambda x: x['n']))

Sample Output: 

5.0
15.0

Flowchart:

Flowchart: Calculate the average of a given list, after mapping each element to a value using the provided function.

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Previous: Write a Python program to convert a given list of dictionaries into a list of values corresponding to the specified key.
Next: Write a Python program to find the value of the first element in the given list that satisfies the provided testing function.

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Python: Tips of the Day

Find current directory and file's directory:

To get the full path to the directory a Python file is contained in, write this in that file:

import os 
dir_path = os.path.dirname(os.path.realpath(__file__))

(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)

To get the current working directory use

import os
cwd = os.getcwd()

Documentation references for the modules, constants and functions used above:

  • The os and os.path modules.
  • The __file__ constant
  • os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
  • os.path.dirname(path) (returns "the directory name of pathname path")
  • os.getcwd() (returns "a string representing the current working directory")
  • os.chdir(path) ("change the current working directory to path")

Ref: https://bit.ly/3fy0R6m