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

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

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[Tut] How to Multiply List Elements by a Number – Top 5 Ways - xSicKxBot - 07-15-2022

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

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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