Query data means requesting specific data from a dataset. If you are familiar with SQL, you must know what it means to query data, but if you use the pandas library in Python, you can still query data from your dataset. So if you want to learn how to query data from a pandas DataFrame in Python, this article is for you. In this article, I will take you through how to query data using Python.
Query Data using Python
If you are familiar with SQL, you must know how to query data from a database using SQL commands. Just like SQL, you can also query data from a pandas DataFrame. The DataFrame.query() method allows us to write commands to query data from a dataset.
In this method, you write commands in strings. Let’s say you have a dataset of columns a, b, c, and d; here, you want to find all the rows where the values of b are greater than a. For this task, the query that you will write is data.query(“b > a”).
I hope you now have understood the query method in pandas DataFrame. Now let’s look at an example of how to query data from a pandas DataFrame. I will first import a dataset for this task:
import pandas as pd data = pd.read_csv("https://raw.githubusercontent.com/amankharwal/Website-data/master/class_grades.csv") print(data.head())
name homewk1 homewk2 midterm partic exam 0 Bhirasri, Silpa 58 70 66 90 95 1 Brookes, John 63 65 74 75 99 2 Carleton, William 57 0 62 90 91 3 Carli, Guido 90 73 59 85 94 4 Cornell, William 73 56 77 95 46
As you can see, the dataset contains marks of students. Here I will use the query method to look at all the rows where the exam marks are less than 50:
print(data.query("exam < 50"))
name homewk1 homewk2 midterm partic exam 4 Cornell, William 73 56 77 95 46
So there is only one row in this dataset where the marks in the exam are less than 50. Now let’s have a look at all the rows where the midterm marks are more than marks in the final exam (exam column):
print(data.query("midterm > exam"))
name homewk1 homewk2 midterm partic exam 4 Cornell, William 73 56 77 95 46 11 Smith, Sophia 70 93 77 75 75 17 Wells, Henry 0 60 68 85 57 18 Wheelock, Lucy 56 56 72 85 54 19 Yale, Elihu 53 71 77 90 59
So this is how you can query data using the Python programming language.
So this is how you can query data from a pandas DataFrame in Python. Query data means requesting specific data from a dataset. You can learn more about the DataFrame.query method from here. I hope you liked this article on how to query data from a pandas DataFrame. Feel free to ask valuable questions in the comments section below.