How to cast an array from one dtype to another using Numpy astype?

Let’s learn how to cast an array from one dtype to another using the Numpy astype function.

Using an astype function

There is an astype Numpy method which allows us to cast from one dtype to another.

In addition to casting an array from one data type to another, you can also cast an array to a specific data type. To do this, you can use the astype function with the dtype parameter. The dtype parameter specifies the data type that you want to cast the array to.

For example, the following code will cast the array my_int_array to the data type np.float64:

import numpy as np

my_int_array = np.array([1, 2, 4, 7, 17, 43, 4, 9])
print(f"My int array: \n {my_int_array}")
print(f"dtype is: {my_int_array.dtype}")

my_float_array = my_int_array.astype(np.float_)
print(f"My float array: \n {my_float_array}")
print(f"dtype is: {my_float_array.dtype}")

As you may notice, the data type changed from integer32 to float64. This is because the astype function has been used in the Python script with np.float_ as a parameter.

In the same way, you can convert other data types. Just remember that it may change your values. Converting from int to float in my example added decimals to the values. Casting from float to int would truncate decimals.

Key takeaways

You can cast an array from one data type to another using the NumPy astype function.
The astype function takes a dtype parameter, which specifies the data type that you want to cast the array to.
If you cast an array to a data type with a smaller precision, the values in the array may be truncated.
If you cast an array to a data type with a larger precision, the values in the array may be rounded.

FAQs

What is the difference between astype and cast?
The astype function and the cast function are both used to cast arrays to different data types. However, the astype function is more general and can be used to cast arrays to any data type, while the cast function can only be used to cast arrays to certain data types.

What is the fastest way to cast an array to a different data type?
The fastest way to cast an array to a different data type is to use the astype function with the copy=False parameter. This will prevent the array from being copied, which can be a bottleneck for large arrays.

What is the most memory efficient way to cast an array to a different data type?
The most memory efficient way to cast an array to a different data type is to use the astype function with the order=’C’ parameter. This will ensure that the array is stored in contiguous memory, which can be important for certain operations.