[Tut] How to Multiply List Elements by a Number – Top 5 Ways

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How to Multiply List Elements by a Number – Top 5 Ways

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Problem Formulation and Solution Overview

In this article, you’ll learn how to multiply List Elements by a Number in Python.

This example multiples the first five (5) Prime Numbers by two (2) and return the result.

Question: How would we write Python code to multiply the list elements?

We can accomplish this task by one of the following options:

• Method 1: Use
  Code:

  List Comprehension
  
  
  
• Method 2: Use
  Code:

  Pandas
  Code:

  tolist()
  
  
  
• Method 3: Use
  Code:

  map()
  and a
  Code:

  lambda()
  
  
  
• Method 4: Use NumPy
  Code:

  Array()
  
  
  
• Method 5: Use
  Code:

  Slicing
  
  

Method 1: Use List Comprehension

This method uses

Code:

List Comprehension

to apply a mathematical operation to each element and return the result.

Code:

prime_nums = [2, 3, 5, 7, 11] mult_result = [x * 2 for x in prime_nums] print(mult_result)

Above declares the first (5) Prime Numbers and saves this

Code:

List

to

Code:

prime_nums

. Next,

Code:

List Comprehension

loops through each element and applies the multiplication operation to each. The output saves to

Code:

mult_result

and is output to the terminal.

Code:

[4, 6, 10, 14, 22]

Method 2: Use Pandas tolist()

This method requires an additional library to be imported,

Code:

Pandas

, to use the

Code:

tolist()

function.

Code:

import pandas as pd prime_nums = [2, 3, 5, 7, 11] mult_result = pd.Series(prime_nums) mult_result = (mult_result*2).tolist() print(mult_result)

Above, imports the

Code:

Pandas

Library. Click here if this requires installation. Then, the first (5) Prime Numbers are declared and saved to

Code:

prime_nums

.

Next,

Code:

prime_nums

is passed as an argument to the

Code:

pd.Series()

function and returns

Code:

mult_result

. The output of

Code:

mult_result

at this point is shown below.

Code:

0 21 32 53 74 11dtype: int64

Now, we need to convert this output to a list (

Code:

tolist()

) and apply the multiplication operation to each element. The results save to

Code:

mult_result

and are output to the terminal.

Code:

[4, 6, 10, 14, 22]

Method 3: Use map and lambda Functions

This method wraps the

Code:

map()

, and

Code:

lambda

functions inside a Python

Code:

List

and calculates the results.

Code:

prime_nums = [2, 3, 5, 7, 11] mult_result = list(map(lambda x: x*2, prime_nums)) print(mult_result)

Above declares the first (5) Prime Numbers and saves them to

Code:

prime_nums

. The next line does the following:

• The
  Code:

  map()
  function is passed the
  Code:

  lambda()
  function as an argument
  Code:

  (map(lambda x: x*2, prime_nums)
  ).
  
  
• The
  Code:

  lambda
  performs the multiplication operation to each element of
  Code:

  prime_nums
  and saves it to
  Code:

  map()
  as an object similar to below.
  
  Code:

  <map object at 0x000001DC99CBBBB0>
  
  
• The
  Code:

  map()
  object is then converted to a
  Code:

  List
  .
  
  
• The results save to
  Code:

  mult_result
  .
  

Then,

Code:

mult_result

is output to the terminal.

Code:

[4, 6, 10, 14, 22]

Method 4: Use Numpy Array()

This method requires an additional library to be imported, NumPy, to use the

Code:

np.array()

function.

Code:

import numpy as np prime_nums = [2, 3, 5, 7, 11] the_result = list(np.array(prime_nums) * 2) print(the_result)

Above, imports the NumPy Library. Click here if this requires installation. Then the first (5) Prime Numbers are declared and saved to

Code:

prime_nums

.

Next,

Code:

prime_nums

is passed as an argument to

Code:

np.array()

where the multiplication operation is applied to each element. Then, this is converted to a List, saved to

Code:

the_result

and output to the terminal.

Code:

[4, 6, 10, 14, 22]

Method 5: Use Slicing

This method uses Python’s infamous

Code:

Slicing

! No overhead, and a very pythonic way to resolve the issue.

Code:

prime_nums = [2, 3, 5, 7, 11] prime_nums[:] = [x * 2 for x in prime_nums] print(prime_nums)

Above declares the first (5) Prime Numbers and saves them to

Code:

prime_nums

.

Then slicing is applied and used in conjunction with

Code:

List Comprehension

to apply the multiplication operation to each element. The results save back to

Code:

prime_nums

and are output to the terminal.

Code:

[4, 6, 10, 14, 22]

A Finxter Favorite!

Summary

These methods of multiplying list elements by a number should give you enough information to select the best one for your coding requirements.

Good Luck & Happy Coding!

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Programmer 1: We have a problem
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Programmer 1: Now we have two problems

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