How to save array as csv file with Numpy?

In this tutorial, we’ll learn how to save a NumPy array as a CSV (Comma Separated Values) file using the savetxt method. Saving data as a CSV file is a common operation in data science and analysis, and NumPy provides a straightforward way to accomplish this.

Using NumPy’s savetxt method

NumPy’s savetxt function lets us save NumPy arrays as text files. We can easily save an array as comma-separated values, creating a CSV file.

To save an array to a CSV file, you need to use savetxt like in the example below:

import numpy as np

my_array = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9]).reshape(3, 3)
np.savetxt("my_matrix.csv", my_array, delimiter=",")

print("CSV file saved successfully!") #Added feedback

Let’s break down the np.savetxt("my_matrix.csv", my_array, delimiter=",") syntax:

• The first argument, "my_matrix.csv", is the file name. You can also specify a full path to the file here (e.g., "path/to/my_matrix.csv" or "C:\\path\\to\\my_matrix.csv" on Windows).
• my_array is the NumPy array you want to save as a CSV.
• delimiter="," specifies the delimiter used to separate values in the CSV file. Since it’s a CSV file, we use a comma.

More Options with savetxt

The savetxt function offers more options for customizing the output:

import numpy as np

my_array = np.array([[1.12345, 2.67890], [3.14159, 4.00001]])

# Formatting floating-point numbers
np.savetxt("formatted_matrix.csv", my_array, delimiter=",", fmt="%.2f") #2 decimal places

# Adding a header and footer
header = "Column 1,Column 2"
footer = "End of data"
np.savetxt("header_footer_matrix.csv", my_array, delimiter=",", header=header, footer=footer, comments='') #comments='' removes the '#' before the header

# Saving integers
int_array = np.array([[1, 2], [3, 4]], dtype=int)
np.savetxt("int_matrix.csv", int_array, delimiter=",", fmt="%d")

#Different delimiter
np.savetxt("tab_separated.txt", my_array, delimiter="\t") #Tab separated

Note that the comments=” argument is crucial when using header and footer. By default, savetxt prefixes comments (including the header and footer) with ‘#’. Setting comments=” suppresses this default comment character, ensuring that the header and footer lines are written as plain text in the CSV file without leading ‘#’ symbols.