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In this tutorial, we will discuss how to store numpy arrays in CSV files.

Using pandasDataFrame to save NumPy arrays in CSV files

In this approach, we will first save the array in pandasa DataFrame and then convert it into a CSV file.

The following code shows how we can achieve this.

import pandas as pd
import numpy as np

a = np.asarray([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
pd.DataFrame(a).to_csv("sample.csv")

pd.DataFrameThe function stores the array in a DataFrame and we just need to_csv()to export it to a CSV file using the function.

Use numpy.savetxt()the function to save NumPy arrays to CSV files

The save function in the numpy module savetxt()can save an array to a text file. We can specify the file format, delimiter, and many other parameters to get the end result in the desired format.

In the following code, we use this function to save the array in a CSV file.

import numpy as np

a = np.asarray([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

np.savetxt("sample.csv", a, delimiter=",")

Use tofile()the function to save NumPy arrays to CSV files

tofile()The function allows us to write arrays to text or binary files. However, this method has many disadvantages. It is more of a convenience function for quickly storing array data. The accuracy of the information is lost because it stores everything in one line, so this method is not a good choice for files intended for archiving data. Some of these problems can be overcome by outputting the data as a text file at the expense of speed and file size.

The following code demonstrates the usage of this function.

import numpy as np

a = np.asarray([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

a.tofile("sample.csv", sep=",")

Save NumPy arrays in CSV files using file processing methods

We can use traditional file processing methods, but they are not recommended because such methods require many modifications depending on the shape of the array and use a lot of memory.

The following code shows an example of this approach.

a = np.asarray([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
csv_rows = ["{},{},{}".format(i, j, k) for i, j, k in a]
csv_text = "\n".join(csv_rows)

with open("sample.csv", "w") as f:
    f.write(csv_text)

We unpack the array into a list of rows and then join()join the list using the function to return a single string. We then write this string to the CSV file.