Multiplying 1D Array in Python
Question:
If I have a 1D array in Python for example:
a = (10,20,30,40,50)
How can I multiply this by an integer for example 2 to produce:
b = (20,40,60,80,100)
I have tried:
b = a*2
But it doesn’t seem to do anything.
Answers:
Tuples are immutable; use lists ([] instead of ()) if you’re going to want to change the contents of the actual array.
To make a new list that has elements twice those of the tuple, loop over the tuple and multiply each element:
b = []
for num in a:
b.append(2*num)
This can be shortened to
b = [2*num for num in a]
using list comprehensions.
Note that If you really want the final result to still be a tuple, you can use use
b = tuple([2*num for num in a])
I believe the closest thing you can get to your original syntax without using third party libraries would be
>>> map(lambda n: n*2, [1,2,3])
[2, 4, 6]
which is basically just a fancy way of saying, “take the function f(n) = 2n and apply if to the list [1,2,3]“.
Use the following:
>>> b = [2 * i for i in a]
>>> b
[20, 40, 60, 80, 100]
a * 2 will duplicate your set:
>>> a = (10,20,30,40,50)
>>> a * 2
(10, 20, 30, 40, 50, 10, 20, 30, 40, 50)
For a more natural way of working with numbers, you may want to consider numpy.
Using numpy, your code would like like this:
import numpy as np
a = np.array([10,20,30,40,50])
b = a*2
If I have a 1D array in Python for example:
a = (10,20,30,40,50)
How can I multiply this by an integer for example 2 to produce:
b = (20,40,60,80,100)
I have tried:
b = a*2
But it doesn’t seem to do anything.
Tuples are immutable; use lists ([] instead of ()) if you’re going to want to change the contents of the actual array.
To make a new list that has elements twice those of the tuple, loop over the tuple and multiply each element:
b = []
for num in a:
b.append(2*num)
This can be shortened to
b = [2*num for num in a]
using list comprehensions.
Note that If you really want the final result to still be a tuple, you can use use
b = tuple([2*num for num in a])
I believe the closest thing you can get to your original syntax without using third party libraries would be
>>> map(lambda n: n*2, [1,2,3])
[2, 4, 6]
which is basically just a fancy way of saying, “take the function f(n) = 2n and apply if to the list [1,2,3]“.
Use the following:
>>> b = [2 * i for i in a]
>>> b
[20, 40, 60, 80, 100]
a * 2 will duplicate your set:
>>> a = (10,20,30,40,50)
>>> a * 2
(10, 20, 30, 40, 50, 10, 20, 30, 40, 50)
For a more natural way of working with numbers, you may want to consider numpy.
Using numpy, your code would like like this:
import numpy as np
a = np.array([10,20,30,40,50])
b = a*2