{"id":126338,"date":"2022-07-07T16:59:52","date_gmt":"2022-07-07T16:59:52","guid":{"rendered":"https:\/\/blog.finxter.com\/?p=459615"},"modified":"2022-07-07T16:59:52","modified_gmt":"2022-07-07T16:59:52","slug":"how-to-convert-a-csv-to-numpy-array-in-python","status":"publish","type":"post","link":"https:\/\/sickgaming.net\/blog\/2022\/07\/07\/how-to-convert-a-csv-to-numpy-array-in-python\/","title":{"rendered":"How to Convert a CSV to NumPy Array in Python?"},"content":{"rendered":"
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5\/5 – (1 vote) <\/div>\n<\/div>\n

Problem Formulation<\/h2>\n

Given a CSV file (e.g., stored in the file with name 'my_file.csv'<\/code>).<\/p>\n

INPUT<\/strong>: file 'my_file.csv'<\/code>\n9,8,7\n6,5,4\n3,2,1<\/code><\/pre>\n
\n
\"How<\/figure>\n<\/div>\n
Challenge<\/strong>: How to convert it to a NumPy Array?<\/p>\n
OUTPUT<\/strong>: 2D NumPy Array<\/code>\n[[9. 8. 7.] [6. 5. 4.] [3. 2. 1.]]<\/code><\/pre>\n
Method 1: np.loadtxt()<\/h2>\n
<\/span>\"\"<\/p>\n
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np.loadtxt()<\/strong><\/p>\n<\/div>\n<\/div>\n
You can convert a CSV file to a NumPy array simply by calling np.loadtxt()<\/a><\/code> with two arguments: the filename<\/code> and the delimiter<\/code> string. For example, the expression np.loadtxt('my_file.csv', delimiter=',')<\/code> returns a NumPy array from the 'my_file.csv'<\/code> with delimiter symbols ','<\/code>. <\/p>\n
Here’s an example:<\/p>\n
import numpy as np array = np.loadtxt('my_file.csv', delimiter=',')\nprint(array)<\/pre>\n
Output:<\/p>\n
[[9. 8. 7.] [6. 5. 4.] [3. 2. 1.]]<\/code><\/pre>\n
Method 2: np.loadtxt() with Header<\/h2>\n
<\/span>\"\"<\/p>\n
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np.loadtxt() + header<\/strong><\/p>\n<\/div>\n<\/div>\n
You can convert a CSV file with first-line header to a NumPy array by calling np.loadtxt()<\/a><\/code> with three arguments: the filename<\/code>, skiprows=1<\/code> to skip the first line (header), and the delimiter<\/code> string. For example, the expression np.loadtxt('my_file.csv', skiprows=1, delimiter=',')<\/code> returns a NumPy array from the 'my_file.csv'<\/code> with delimiter symbols ','<\/code> while skipping the first line.<\/p>\n
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\"\"
Figure<\/strong>: Skip the first header line in the CSV using the skiprows<\/code> argument of the np.loadtxt()<\/code> function.<\/em><\/figcaption><\/figure>\n<\/div>\n
Here’s an example:<\/p>\n
import numpy as np array = np.loadtxt('my_file.csv', skiprows=1, delimiter=',')\nprint(array)<\/pre>\n
Output:<\/p>\n
[[9. 8. 7.] [6. 5. 4.] [3. 2. 1.]]<\/code><\/pre>\n
Method 3: CSV Reader<\/h2>\n
<\/span>\"\"<\/p>\n
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CSV Reader<\/strong><\/p>\n<\/div>\n<\/div>\n
To convert a CSV file 'my_file.csv'<\/code> into a list of lists in Python, use the csv.reader(file_obj)<\/code> method to create a CSV file reader. Then convert the resulting object to a list using the list()<\/a><\/code> constructor. As a final step, you can convert the nested list to a NumPy array by using the np.array(list)<\/code> constructor.<\/p>\n
Here’s an example:<\/p>\n
import numpy as np\nimport csv csv_filename = 'my_file.csv' with open(csv_filename) as f: reader = csv.reader(f) lst = list(reader) print(lst)<\/pre>\n
The output is the list of lists<\/a>:<\/p>\n
[['9', '8', '7'], ['6', '5', '4'], ['3', '2', '1']]<\/code><\/pre>\n
Now, if you need to convert it to a NumPy array, you can simply use the np.array()<\/code> function on the newly-created list like so:<\/p>\n
array = np.array(lst)\nprint(array)<\/pre>\n
Output:<\/p>\n
[['9' '8' '7'] ['6' '5' '4'] ['3' '2' '1']]<\/code><\/pre>\n
\"\ud83c\udf0e\" Related Tutorial<\/strong>: How to Convert CSV to List of Lists in Python<\/a><\/p>\n
Method 4: np.genfromtxt()<\/h2>\n
<\/span>\"\"<\/p>\n
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np.genfromtxt()<\/strong><\/p>\n<\/div>\n<\/div>\n
You can convert a CSV file to a NumPy array simply by calling np.genfromtxt()<\/code><\/a> with two arguments: the filename<\/code> and the delimiter<\/code> string. For example, the expression np.genfromtxt('my_file.csv', delimiter=',')<\/code> returns a NumPy array from the 'my_file.csv'<\/code> with delimiter symbol ','<\/code>. <\/p>\n
Here’s an example:<\/p>\n
import numpy as np array = np.loadtxt('my_file.csv', delimiter=',')\nprint(array)<\/pre>\n
Output:<\/p>\n
[[9. 8. 7.] [6. 5. 4.] [3. 2. 1.]]<\/code><\/pre>\n
Method 5: Pandas read_csv() and df.to_numpy()<\/h2>\n
<\/span>\"\"<\/p>\n
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read_csv() and df.to_numpy()<\/strong><\/p>\n<\/div>\n<\/div>\n
A quick and efficient way to read a CSV to a NumPy array is to combine Pandas’ pd.read_csv()<\/a><\/code> function to read a given CSV file to a DataFrame with the df.to_numpy()<\/a><\/code> function to convert the Pandas DataFrame to a NumPy array.<\/p>\n
Here’s an example:<\/p>\n
import pandas as pd df = pd.read_csv('my_file.csv', header=None)\narray = df.to_numpy() print(array)\n<\/pre>\n
Output:<\/p>\n
[[9 8 7] [6 5 4] [3 2 1]]<\/code><\/pre>\n
\"\ud83c\udf0e\" Related Tutorial<\/strong>: 17 Ways to Read a CSV File to a Pandas DataFrame<\/a><\/p>\n
Summary<\/h2>\n
We have seen five ways to convert a CSV file to a 2D NumPy array:<\/p>\n
    \n
  • Method 1<\/strong>: np.loadtxt()<\/code><\/li>\n
  • Method 2<\/strong>: np.loadtxt()<\/code> with Header<\/li>\n
  • Method 3<\/strong>: CSV Reader<\/li>\n
  • Method 4<\/strong>: np.genfromtxt()<\/code><\/li>\n
  • Method 5<\/strong>: Pandas read_csv()<\/code> and df.to_numpy()<\/code><\/li>\n<\/ul>\n
    Our preferred way is np.loadtxt()<\/code> for its simplicity and Pandas for its extensibility.<\/p>\n","protected":false},"excerpt":{"rendered":"
    5\/5 – (1 vote) Problem Formulation Given a CSV file (e.g., stored in the file with name ‘my_file.csv’). INPUT: file ‘my_file.csv’ 9,8,7 6,5,4 3,2,1 Challenge: How to convert it to a NumPy Array? OUTPUT: 2D NumPy Array [[9. 8. 7.] [6. 5. 4.] [3. 2. 1.]] Method 1: np.loadtxt() np.loadtxt() You can convert a CSV […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[857],"tags":[73,468,528],"class_list":["post-126338","post","type-post","status-publish","format-standard","hentry","category-python-tut","tag-programming","tag-python","tag-tutorial"],"_links":{"self":[{"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/posts\/126338","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/comments?post=126338"}],"version-history":[{"count":0,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/posts\/126338\/revisions"}],"wp:attachment":[{"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/media?parent=126338"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/categories?post=126338"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sickgaming.net\/blog\/wp-json\/wp\/v2\/tags?post=126338"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}