How to Read CSV to NumPy Array in Python

1. Use the numpy.genfromtxt() Function to Read CSV Data to a NumPy Array
2. Use a pandas DataFrame to Read CSV Data to a NumPy Array
3. Use the csv Module to Read CSV Data to a NumPy Array

This tutorial will discuss how to read data from a CSV file and store it in a numpy array.

Use the numpy.genfromtxt() Function to Read CSV Data to a NumPy Array

The genfromtxt() function is frequently used to load data from text files. We can read data from CSV files using this function and store it in a numpy array. This function has many arguments available, making it easier to load the data in our desired format. We can specify the delimiter, deal with missing values, delete specified characters, and specify the datatype of the data using the different arguments of this function.

For example,

from numpy import genfromtxt

data = genfromtxt("sample.csv", delimiter=",", skip_header=1)
print(data)

Output:

[[1. 2. 3.]
 [4. 5. 6.]]

Many other functions are derived from this, like recfromtxt() and recfromcsv() that can perform the same function but have different default values.

In the following code, we will read data from a CSV file using the recfromcsv() file.

import numpy as np

data = np.recfromcsv("sample.csv", skip_header=0)
print(data)

Output:

[(1, 2, 3) (4, 5, 6)]

Note that we didn’t have to specify the delimiter as a comma and the different value to specify the header row.

Use a pandas DataFrame to Read CSV Data to a NumPy Array

We can also make use of a pandas DataFrame to read CSV data into an array. For this, we will read the data to a DataFrame and then convert this to a NumPy array using the values() function from the pandas library.

The following code implements this.

from pandas import read_csv

df = read_csv("sample.csv")
data = df.values
print(data)

Output:

[[1 2 3]
 [4 5 6]]

Use the csv Module to Read CSV Data to a NumPy Array

The csv module is used to read and write data to CSV files efficiently. This method will read the data from a CSV file using this module and store it in a list. We will then proceed to convert this list to a numpy array.

The code below will explain this.

import csv
import numpy as np

with open("sample.csv", "r") as f:
    data = list(csv.reader(f, delimiter=";"))

data = np.array(data)
print(data)

Output:

[['1,2,3']
 ['4,5,6']]