• Group data by a column.

df.groupby('col1')

• Group by a column and get the sum.

df.groupby('col1').sum()

• Apply multiple aggregation functions at once.

df.groupby('col1').agg(['mean', 'count'])

• Get the size of each group.

df.groupby('col1').size()

• Get the frequency counts of unique values in a Series.

df['col1'].value_counts()

• Create a pivot table.

pd.pivot_table(df, values='D', index=['A', 'B'], columns=['C'])

VI. Merging, Joining & Concatenating

• Merge two DataFrames (like a SQL join).

pd.merge(left_df, right_df, on='key_column')

• Concatenate (stack) DataFrames along an axis.

pd.concat([df1, df2]) # Stacks rows

• Join DataFrames on their indexes.

left_df.join(right_df, how='outer')

VII. Input & Output

• Write a DataFrame to a CSV file.

df.to_csv('output.csv', index=False)

• Write a DataFrame to an Excel file.

df.to_excel('output.xlsx', sheet_name='Sheet1')

• Read data from an Excel file.

pd.read_excel('input.xlsx', sheet_name='Sheet1')

• Read from a SQL database.

pd.read_sql_query('SELECT * FROM my_table', connection_object)

VIII. Time Series & Special Operations

• Use the string accessor (.str) for Series operations.

s.str.lower()
s.str.contains('pattern')

• Use the datetime accessor (.dt) for Series operations.

s.dt.year
s.dt.day_name()

• Create a rolling window calculation.

df['col1'].rolling(window=3).mean()

• Create a basic plot from a Series or DataFrame.

df['col1'].plot(kind='hist')

#Python #Pandas #DataAnalysis #DataScience #Programming

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By: @DataScienceM ✨

• (Time: 90s) Simpson's Paradox occurs when:
a) A model performs well on training data but poorly on test data.
b) Two variables appear to be correlated, but the correlation is caused by a third variable.
c) A trend appears in several different groups of data but disappears or reverses when these groups are combined.
d) The mean, median, and mode of a distribution are all the same.

• (Time: 75s) When presenting your findings to non-technical stakeholders, you should focus on:
a) The complexity of your statistical models and the p-values.
b) The story the data tells, the business implications, and actionable recommendations.
c) The exact Python code and SQL queries you used.
d) Every single chart and table you produced during EDA.

• (Time: 75s) A survey about job satisfaction is only sent out via a corporate email newsletter. The results may suffer from what kind of bias?
a) Survivorship bias
b) Selection bias
c) Recall bias
d) Observer bias

• (Time: 90s) For which of the following machine learning algorithms is feature scaling (e.g., normalization or standardization) most critical?
a) Decision Trees and Random Forests.
b) K-Nearest Neighbors (KNN) and Support Vector Machines (SVM).
c) Naive Bayes.
d) All algorithms require feature scaling to the same degree.

• (Time: 90s) A Root Cause Analysis for a business problem primarily aims to:
a) Identify all correlations related to the problem.
b) Assign blame to the responsible team.
c) Build a model to predict when the problem will happen again.
d) Move beyond symptoms to find the fundamental underlying cause of the problem.

• (Time: 75s) A "funnel analysis" is typically used to:
a) Segment customers into different value tiers.
b) Understand and optimize a multi-step user journey, identifying where users drop off.
c) Forecast future sales.
d) Perform A/B tests on a website homepage.

• (Time: 75s) Tracking the engagement metrics of users grouped by their sign-up month is an example of:
a) Funnel Analysis
b) Regression Analysis
c) Cohort Analysis
d) Time-Series Forecasting

• (Time: 90s) A retail company wants to increase customer lifetime value (CLV). A data-driven first step would be to:
a) Redesign the company logo.
b) Increase the price of all products.
c) Perform customer segmentation (e.g., using RFM analysis) to understand the behavior of different customer groups and tailor strategies accordingly.
d) Switch to a new database provider.

#DataAnalysis #Certification #Exam #Advanced #SQL #Pandas #Statistics #MachineLearning

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By: @DataScienceM ✨

📌 The Absolute Beginner’s Guide to Pandas DataFrames

🗂 Category: DATA SCIENCE

🕒 Date: 2025-11-17 | ⏱️ Read time: 5 min read

New to the Pandas library? This beginner's guide covers the fundamental skill of creating DataFrames. Learn the essential techniques to initialize a DataFrame from common Python data structures, including dictionaries, lists, and NumPy arrays. Mastering this core concept is the perfect first step for anyone starting their data analysis journey in Python.

#Python #Pandas #DataAnalysis #DataFrames

📌 I Cleaned a Messy CSV File Using Pandas .  Here’s the Exact Process I Follow Every Time.

🗂 Category: DATA SCIENCE

🕒 Date: 2025-11-26 | ⏱️ Read time: 17 min read

Stop guessing when cleaning messy CSV files. This article details a repeatable 5-step workflow using Python's Pandas library to systematically diagnose and fix data quality issues. Learn a structured, practical process to transform your data preparation, moving from haphazard fixes to a reliable methodology for any data professional.

#Python #Pandas #DataCleaning #DataScience