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Data Analyst Interview Questions with Answers: Part-3 ๐Ÿง ๐Ÿ“Š

21. What is correlation vs causation?
โ€ข Correlation is a statistical relationship between two variables (e.g., ice cream sales temperature).
โ€ข Causation means one variable directly affects another (e.g., smoking causes lung disease).
Correlation doesnโ€™t imply causation.

22. What is regression analysis?
Itโ€™s used to predict the value of a dependent variable based on one or more independent variables.
Example: Predicting sales based on ad spend using linear regression.

23. What is hypothesis testing?
A statistical method to determine if thereโ€™s enough evidence to support a claim about a dataset.
It involves:
โ€ข Null hypothesis (H0): no effect
โ€ข Alternative hypothesis (H1): there is an effect
Results are judged based on significance level (usually 0.05).

24. What is p-value and its importance?
P-value indicates the probability of getting observed results if H0 is true.
โ€ข Low p-value (< 0.05) โ†’ Reject H0 โ†’ Significant result
โ€ข High p-value (> 0.05) โ†’ Fail to reject H0
It helps assess if differences are due to chance.

25. What is A/B testing?
A/B testing compares two versions (A and B) to see which performs better.
Common in marketing and UX: e.g., comparing two landing page designs for conversion rates.

26. What is a confidence interval?
It gives a range within which we expect a population parameter to fall, with a certain level of confidence (e.g., 95%).
Example: โ€œWeโ€™re 95% confident the average age of users is between 24โ€“27.โ€

27. What is outlier detection and how do you handle it?
Outliers are data points that deviate significantly from others.
Methods to detect:
โ€ข Z-score
โ€ข IQR method
โ€ข Box plots
Handle by:
โ€ข Removing
โ€ข Imputing
โ€ข Investigating cause

28. Explain standard deviation and variance
โ€ข Variance measures how far values spread out from the mean.
โ€ข Standard deviation is the square root of variance, representing dispersion in original units.
Low SD โ†’ data close to mean; High SD โ†’ more spread out.

29. What is a pivot table?
A pivot table summarizes data for analysis, often used in Excel or Power BI.
You can group, filter, and aggregate data (e.g., total sales by region and product).

30. How do you visualize time series data?
Use line charts, area charts, or time-based plots.
Include trend lines, moving averages, and seasonal decomposition to analyze patterns over time.

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๐Ÿง ๐Ÿ“Š Data Analyst Interview Questions with Answers: Part-4

31. What is ETL process? ๐Ÿ”„
ETL stands for Extract, Transform, Load.
- Extract: Pulling data from sources (databases, APIs, files) ๐Ÿ“ค
- Transform: Cleaning, formatting, and applying business logic ๐Ÿ› ๏ธ
- Load: Saving the transformed data into a data warehouse or system ๐Ÿ“ฅ
It helps consolidate data for reporting and analysis.

32. What are some challenges in data cleaning? ๐Ÿšซ
- Missing values ๐Ÿคท
- Duplicates ๐Ÿ‘ฏ
- Inconsistent formats (e.g., date formats, units) ๐Ÿงฉ
- Outliers ๐Ÿ“ˆ
- Incorrect or incomplete data โŒ
- Merging data from multiple sources ๐Ÿค
Cleaning is time-consuming but critical for accurate analysis.

33. What is data wrangling? ๐Ÿงน
Also known as data munging, itโ€™s the process of transforming raw data into a usable format.
Includes:
- Cleaning โœจ
- Reshaping ๐Ÿ“
- Combining datasets ๐Ÿ”—
- Dealing with missing values or outliers ๐Ÿ—‘๏ธ

34. How do you handle missing data? โ“
- Remove rows/columns (if missingness is high) โœ‚๏ธ
- Imputation (mean, median, mode) ๐Ÿ”ข
- Forward/backward fill โžก๏ธโฌ…๏ธ
- Using models (KNN, regression) ๐Ÿค–
- Always analyze why data is missing before deciding.

35. What is data normalization in Python? โš–๏ธ
Normalization scales numerical data to a common range (e.g., 0 to 1).
Common methods:
from sklearn.preprocessing import MinMaxScaler
scaler = MinMaxScaler()
normalized_data = scaler.fit_transform(data)

Useful for ML models to prevent bias due to varying value scales.

36. Difference between .loc and .iloc in Pandas ๐Ÿ“๐Ÿ”ข
- .loc[]: Label-based indexing

  df.loc[2]       # Row with label 2
df.loc[:, 'age'] # All rows, 'age' column

- .iloc[]: Integer position-based indexing

  df.iloc[2]      # Third row
df.iloc[:, 1] # All rows, second column


37. How do you merge dataframes in Pandas? ๐Ÿค
Using merge() or concat()
pd.merge(df1, df2, on='id', how='inner')  # SQL-style joins
pd.concat([df1, df2], axis=0) # Stack rows

Choose keys and join types (inner, left, outer) based on data structure.

38. Explain groupby() in Pandas ๐Ÿ“Š
Used to group data and apply aggregation.
df.groupby('category')['sales'].sum()

Steps:
1. Split data into groups ๐Ÿงฉ
2. Apply function (sum, mean, count) ๐Ÿงฎ
3. Combine result ๐Ÿ“ˆ

39. What are NumPy arrays? โž•
N-dimensional arrays used for fast numeric computation.
Faster than Python lists and support vectorized operations.
import numpy as np
a = np.array([1, 2, 3])


40. How to handle large datasets efficiently? ๐Ÿš€
- Use chunking (read_csv(..., chunksize=10000))
- Use NumPy or Dask for faster ops
- Filter unnecessary columns early
- Use vectorized operations instead of loops
- Work with cloud data tools (BigQuery, Spark)

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โœ… Top Data Analyst Interview Questions with Answers: Part-5 ๐Ÿ“Š๐Ÿ’ผ

41. What is the difference between Python and R for data analysis?
Python: General-purpose language with strong libraries for data (Pandas, NumPy), ML (scikit-learn), and visualization (matplotlib, seaborn). Ideal for production and integration tasks.
R: Built specifically for statistics and data visualization. Excellent for statistical modeling, academic use, and reports.
Summary: Python = versatility scalability. R = deep statistical analysis.

42. Explain the use of matplotlib/seaborn
matplotlib: A low-level Python library for creating static, animated, and interactive plots.
Example: plt.plot(x, y)
seaborn: Built on top of matplotlib; used for more attractive and informative statistical graphics.
Example: sns.barplot(x, y, data=df)
Use Case: Quick, clean charts for dashboards and presentations.

43. What are KPIs and why are they important?
KPIs (Key Performance Indicators) are measurable values that show how effectively a company is achieving key business objectives.
Examples:
โ€ข Conversion rate
โ€ข Customer churn
โ€ข Average order value
They help teams track progress, adjust strategies, and communicate success.

44. What is a dashboard and how do you design one?
A dashboard is a visual interface displaying data insights using charts, tables, and KPIs.
Design principles:
โ€ข Keep it clean and focused
โ€ข Highlight key metrics
โ€ข Use filters for interactivity
โ€ข Make it responsive
Tools: Power BI, Tableau, Looker, etc.

45. What is storytelling with data?
Itโ€™s about presenting data in a narrative way to help stakeholders make decisions.
Includes:
โ€ข Clear visuals
โ€ข Business context
โ€ข Insights + actions
Goal: Make complex data understandable and impactful.

46. How do you prioritize tasks in a data project?
Use a combination of:
โ€ข Impact vs effort matrix
โ€ข Business value
โ€ข Deadlines
Also clarify objectives with stakeholders before diving deep.

47. How do you ensure data quality and accuracy?
โ€ข Validate sources
โ€ข Handle missing duplicate data
โ€ข Use constraints (e.g., data types)
โ€ข Create audit rules (e.g., balance = credit - debit)
โ€ข Document data flows

48. Explain a challenging data problem you've solved
(Example) โ€œI had to clean a messy customer dataset with inconsistent formats, missing values, and duplicate IDs. I wrote Python scripts using Pandas to clean, standardize, and validate the data, which was later used in a Power BI dashboard by the marketing team.โ€

49. How do you present findings to non-technical stakeholders?
โ€ข Use simple language
โ€ข Avoid jargon
โ€ข Use visuals (bar charts, trends, KPIs)
โ€ข Focus on impact and next steps
โ€ข Tell a story with data instead of dumping numbers

50. What are your favorite data tools and why?
โ€ข Python: For flexibility and automation
โ€ข Power BI: For interactive reporting
โ€ข SQL: For powerful data extraction
โ€ข Jupyter Notebooks: For documenting and sharing analysis
Tool preference depends on the projectโ€™s needs.

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โœ… If you're serious about learning Data Analytics โ€” follow this roadmap ๐Ÿ“Š๐Ÿง 

1. Learn Excel basics โ€“ formulas, pivot tables, charts
2. Master SQL โ€“ SELECT, JOIN, GROUP BY, CTEs, window functions
3. Get good at Python โ€“ especially Pandas, NumPy, Matplotlib, Seaborn
4. Understand statistics โ€“ mean, median, standard deviation, correlation, hypothesis testing
5. Clean and wrangle data โ€“ handle missing values, outliers, normalization, encoding
6. Practice Exploratory Data Analysis (EDA) โ€“ univariate, bivariate analysis
7. Work on real datasets โ€“ sales, customer, finance, healthcare, etc.
8. Use Power BI or Tableau โ€“ create dashboards and data stories
9. Learn business metrics KPIs โ€“ retention rate, CLV, ROI, conversion rate
10. Build mini-projects โ€“ sales dashboard, HR analytics, customer segmentation
11. Understand A/B Testing โ€“ setup, analysis, significance
12. Practice SQL + Python combo โ€“ extract, clean, visualize, analyze
13. Learn about data pipelines โ€“ basic ETL concepts, Airflow, dbt
14. Use version control โ€“ Git GitHub for all projects
15. Document your analysis โ€“ use Jupyter or Notion to explain insights
16. Practice storytelling with data โ€“ explain โ€œso what?โ€ clearly
17. Know how to answer business questions using data
18. Explore cloud tools (optional) โ€“ BigQuery, AWS S3, Redshift
19. Solve case studies โ€“ product analysis, churn, marketing impact
20. Apply for internships/freelance โ€“ gain experience + build resume
21. Post your projects on GitHub or portfolio site
22. Prepare for interviews โ€“ SQL, Python, scenario-based questions
23. Keep learning โ€“ YouTube, courses, Kaggle, LinkedIn Learning

๐Ÿ’ก Tip: Focus on building 3โ€“5 strong projects and learn to explain them in interviews.

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โœ… Top Data Analytics Interview Questions with Answers โ€“ Part 1 ๐Ÿง ๐Ÿ“ˆ

1๏ธโƒฃ What is the difference between Data Analytics and Data Science?
Data Analytics focuses on analyzing existing data to find trends and insights.
Data Science includes analytics but adds machine learning, statistical modeling predictions.

2๏ธโƒฃ What is the difference between structured and unstructured data?
โ€ข Structured: Organized (tables, rows, columns) โ€“ e.g., Excel, SQL DB
โ€ข Unstructured: No fixed format โ€“ e.g., images, videos, social media posts

3๏ธโƒฃ What is Data Cleaning? Why is it important?
Removing or correcting inaccurate, incomplete, or irrelevant data.
It ensures accurate analysis, better decision-making, and model performance.

4๏ธโƒฃ Explain VLOOKUP and Pivot Tables in Excel.
โ€ข VLOOKUP: Searches for a value in a column and returns a value in the same row from another column.
โ€ข Pivot Table: Summarizes data by categories (grouping, totals, averages).

5๏ธโƒฃ What is SQL JOIN?
Combines rows from two or more tables based on a related column.
Types: INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN.

6๏ธโƒฃ What is EDA (Exploratory Data Analysis)?
Itโ€™s the process of visually and statistically exploring datasets to understand their structure, patterns, and anomalies.

7๏ธโƒฃ Difference between COUNT(), SUM(), AVG(), MIN(), MAX() in SQL?
These are aggregate functions used to perform calculations on columns.

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โœ… Top Data Analytics Interview Questions with Answers โ€“ Part 2 ๐Ÿง ๐Ÿ“Š

8๏ธโƒฃ What is data normalization?
Itโ€™s the process of scaling data to fit within a specific range (like 0 to 1) to improve model performance or consistency in analysis.

9๏ธโƒฃ What are KPIs?
Key Performance Indicators โ€“ measurable values used to track performance against objectives (e.g., revenue, conversion rate, churn rate).

๐Ÿ”Ÿ What is the difference between INNER JOIN and LEFT JOIN?
โ€ข INNER JOIN: Returns records with matching values in both tables.
โ€ข LEFT JOIN: Returns all records from the left table and matched ones from the right (NULLs if no match).

1๏ธโƒฃ1๏ธโƒฃ What is a dashboard in data analytics?
A visual representation of key metrics and data points using charts, graphs, and KPIs to support decision-making.

1๏ธโƒฃ2๏ธโƒฃ What are outliers and how do you handle them?
Outliers are data points far from others. Handle them by:
โ€ข Removing
โ€ข Capping
โ€ข Using robust statistical methods
โ€ข Transformation (e.g., log)

1๏ธโƒฃ3๏ธโƒฃ What is correlation analysis?
It measures the relationship between two variables. Values range from -1 to 1. Closer to ยฑ1 means stronger correlation.

1๏ธโƒฃ4๏ธโƒฃ Difference between correlation and causation?
โ€ข Correlation: Two variables move together.
โ€ข Causation: One variable *causes* the other to change.

1๏ธโƒฃ5๏ธโƒฃ What is data storytelling?
Itโ€™s presenting insights from data in a compelling narrative using visuals, context, and recommendations.

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โœ… Top Data Analytics Interview Questions with Answers โ€“ Part 3 ๐Ÿ“Š๐Ÿง 

1๏ธโƒฃ6๏ธโƒฃ What is data cleaning?
The process of fixing or removing incorrect, corrupted, or incomplete data to ensure quality and reliability in analysis.

1๏ธโƒฃ7๏ธโƒฃ What is EDA (Exploratory Data Analysis)?
Itโ€™s the initial step in data analysis where we explore, summarize, and visualize data to understand patterns, outliers, or relationships.

1๏ธโƒฃ8๏ธโƒฃ What is the difference between structured and unstructured data?
โ€ข Structured: Organized in tables (e.g., SQL databases).
โ€ข Unstructured: No fixed format (e.g., text, images, videos).

1๏ธโƒฃ9๏ธโƒฃ What is a data pipeline?
A series of steps to collect, process, and move data from one system to another โ€” often automated.

2๏ธโƒฃ0๏ธโƒฃ Explain the difference between OLAP and OLTP.
โ€ข OLAP (Online Analytical Processing): For complex queries reporting.
โ€ข OLTP (Online Transaction Processing): For real-time transactions.

2๏ธโƒฃ1๏ธโƒฃ What is a dimension vs. a measure in data analysis?
โ€ข Dimension: Descriptive attribute (e.g., Country, Product)
โ€ข Measure: Numeric value you analyze (e.g., Sales, Profit)

2๏ธโƒฃ2๏ธโƒฃ What is data validation?
The process of ensuring data is accurate and clean before analysis or input into systems.

2๏ธโƒฃ3๏ธโƒฃ What is cross-tabulation?
A table that shows the relationship between two categorical variables (often used in Excel or Power BI).

2๏ธโƒฃ4๏ธโƒฃ What is the Pareto principle in data analysis?
Also called 80/20 rule โ€” 80% of effects come from 20% of causes (e.g., 20% of products generate 80% of sales).

2๏ธโƒฃ5๏ธโƒฃ What is drill-down in dashboards?
An interactive feature allowing users to go from summary-level data to detailed-level data by clicking.

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๐Ÿš€ Roadmap to Master Data Analytics in 50 Days! ๐Ÿ“Š๐Ÿ“ˆ

๐Ÿ“… Week 1โ€“2: Foundations
๐Ÿ”น Day 1โ€“3: What is Data Analytics? Tools overview
๐Ÿ”น Day 4โ€“7: Excel/Google Sheets (formulas, pivot tables, charts)
๐Ÿ”น Day 8โ€“10: SQL basics (SELECT, WHERE, JOIN, GROUP BY)

๐Ÿ“… Week 3โ€“4: Programming Data Handling
๐Ÿ”น Day 11โ€“15: Python for data (variables, loops, functions)
๐Ÿ”น Day 16โ€“20: Pandas, NumPy โ€“ data cleaning, filtering, aggregation

๐Ÿ“… Week 5โ€“6: Visualization EDA
๐Ÿ”น Day 21โ€“25: Data visualization (Matplotlib, Seaborn)
๐Ÿ”น Day 26โ€“30: Exploratory Data Analysis โ€“ ask questions, find trends

๐Ÿ“… Week 7โ€“8: BI Tools Advanced Skills
๐Ÿ”น Day 31โ€“35: Power BI / Tableau โ€“ dashboards, filters, DAX
๐Ÿ”น Day 36โ€“40: Real-world case studies โ€“ sales, HR, marketing data

๐ŸŽฏ Final Stretch: Projects Career Prep
๐Ÿ”น Day 41โ€“45: Capstone projects (end-to-end analysis + report)
๐Ÿ”น Day 46โ€“48: Resume, GitHub portfolio, LinkedIn optimization
๐Ÿ”น Day 49โ€“50: Mock interviews + SQL + Excel + scenario questions

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โœ… Data Analytics Foundations: Part-1 ๐Ÿ“Š๐Ÿ’ป

๐Ÿ” What is Data Analytics?
Itโ€™s the process of examining data to uncover insights, trends, and patterns to support decision-making.

๐Ÿ“Œ 4 Key Types of Data Analytics:

1๏ธโƒฃ Descriptive Analytics โ€“ What happened?
โ†’ Summarizes past data (e.g., sales reports)

2๏ธโƒฃ Diagnostic Analytics โ€“ Why did it happen?
โ†’ Identifies causes/trends behind outcomes

3๏ธโƒฃ Predictive Analytics โ€“ What might happen next?
โ†’ Uses models to forecast future outcomes

4๏ธโƒฃ Prescriptive Analytics โ€“ What should we do?
โ†’ Recommends actions based on data insights

๐Ÿงฐ Popular Tools in Data Analytics:

1. Excel / Google Sheets
โ†’ Basics of data cleaning, formulas, pivot tables

2. SQL
โ†’ Extract, join, and filter data from databases

3. Power BI / Tableau
โ†’ Create dashboards and visual reports

4. Python (Pandas, NumPy, Matplotlib)
โ†’ Automate tasks, analyze large datasets, visualize insights

5. R
โ†’ Statistical analysis and data modeling

6. Google Data Studio
โ†’ Simple, free tool for creating interactive dashboards

7. SAS / SPSS (for statistical work)
โ†’ Used in healthcare, finance, and academic sectors

๐Ÿ“ˆ Basic Skills Needed:

โ€ข Data cleaning & preparation
โ€ข Data visualization
โ€ข Statistical analysis
โ€ข Business understanding
โ€ข Storytelling with data

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โœ… Data Analytics Foundations Part-2: Excel for Data Analytics ๐Ÿ“Š๐Ÿงฎ

Excel is one of the most accessible and powerful tools for data cleaning, analysis, and quick visualizationsโ€”great for beginners and pros alike.

๐Ÿ“Œ Key Excel Features for Data Analytics:

1๏ธโƒฃ Formulas  Functions 
โ€ข SUM(), AVERAGE(), COUNT() โ€“ Basic calculations 
โ€ข IF(), VLOOKUP(), INDEX-MATCH() โ€“ Conditional logic  lookups 
โ€ข TEXT(), LEFT(), RIGHT() โ€“ Data formatting

2๏ธโƒฃ Pivot Tables 
โ€ข Summarize large datasets in seconds 
โ€ข Drag  drop to create custom reports 
โ€ข Group, filter, and sort easily

3๏ธโƒฃ Charts  Visualizations 
โ€ข Column, Line, Pie, and Combo charts 
โ€ข Use sparklines for quick trends 
โ€ข Add slicers for interactivity

4๏ธโƒฃ Data Cleaning Tools 
โ€ข Remove duplicates 
โ€ข Text to columns 
โ€ข Flash Fill for auto-pattern detection

5๏ธโƒฃ Data Analysis ToolPak 
โ€ข Run regression, t-tests, and more (enable from Add-ins)

6๏ธโƒฃ Conditional Formatting 
โ€ข Highlight trends, outliers, and specific values visually

7๏ธโƒฃ Filters  Sort 
โ€ข Organize and explore subsets of data quickly

๐Ÿ’ก Pro Tip: Use tables (Ctrl + T) to auto-expand formulas, enable filtering, and apply structured references.

Excel Resources: https://whatsapp.com/channel/0029VaifY548qIzv0u1AHz3i

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โœ… Python Basics for Data Analytics ๐Ÿ“Š๐Ÿ

Python is one of the most in-demand languages for data analytics due to its simplicity, flexibility, and powerful libraries. Here's a detailed guide to get you started with the basics:

๐Ÿง  1. Variables Data Types
You use variables to store data.

name = "Alice"        # String  
age = 28 # Integer
height = 5.6 # Float
is_active = True # Boolean

Use Case: Store user details, flags, or calculated values.

๐Ÿ”„ 2. Data Structures

โœ… List โ€“ Ordered, changeable
fruits = ['apple', 'banana', 'mango']  
print(fruits[0]) # apple

โœ… Dictionary โ€“ Key-value pairs
person = {'name': 'Alice', 'age': 28}  
print(person['name']) # Alice

โœ… Tuple Set
Tuples = immutable, Sets = unordered unique

โš™๏ธ 3. Conditional Statements
score = 85  
if score >= 90:
print("Excellent")
elif score >= 75:
print("Good")
else:
print("Needs improvement")

Use Case: Decision making in data pipelines

๐Ÿ” 4. Loops
For loop
for fruit in fruits:  
print(fruit)


While loop
count = 0  
while count < 3:
print("Hello")
count += 1

๐Ÿ”ฃ 5. Functions
Reusable blocks of logic

def add(x, y):  
return x + y

print(add(10, 5)) # 15

๐Ÿ“‚ 6. File Handling
Read/write data files

with open('data.txt', 'r') as file:  
content = file.read()
print(content)

๐Ÿงฐ 7. Importing Libraries
import pandas as pd  
import numpy as np
import matplotlib.pyplot as plt

Use Case: These libraries supercharge Python for analytics.

๐Ÿงน 8. Real Example: Analyzing Data
import pandas as pd  

df = pd.read_csv('sales.csv') # Load data
print(df.head()) # Preview

# Basic stats
print(df.describe())
print(df['Revenue'].mean())


๐ŸŽฏ Why Learn Python for Data Analytics?
โœ… Easy to learn
โœ… Huge library support (Pandas, NumPy, Matplotlib)
โœ… Ideal for cleaning, exploring, and visualizing data
โœ… Works well with SQL, Excel, APIs, and BI tools

Python Programming: https://whatsapp.com/channel/0029VaiM08SDuMRaGKd9Wv0L

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๐—™๐—ฅ๐—˜๐—˜ ๐—ข๐—ป๐—น๐—ถ๐—ป๐—ฒ ๐— ๐—ฎ๐˜€๐˜๐—ฒ๐—ฟ๐—ฐ๐—น๐—ฎ๐˜€๐˜€ ๐—•๐˜† ๐—œ๐—ป๐—ฑ๐˜‚๐˜€๐˜๐—ฟ๐˜† ๐—˜๐˜…๐—ฝ๐—ฒ๐—ฟ๐˜๐˜€ ๐Ÿ˜

Roadmap to land your dream job in top product-based companies

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- 90-Day Placement Plan
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https://pdlink.in/3Ltb3CE

Date & Time:- 06th January 2026 , 7PM
โค2
โœ… Exploratory Data Analysis (EDA) ๐Ÿ”๐Ÿ“Š

EDA is the first and most important step in any data analytics or machine learning project. It helps you understand the data, spot patterns, detect outliers, and prepare for modeling.

1๏ธโƒฃ Load and Understand the Data
import pandas as pd

df = pd.read_csv("sales_data.csv")
print(df.head())
print(df.shape)

Goal: Get the structure (rows, columns), data types, and sample values.

2๏ธโƒฃ Summary and Info
df.info()
df.describe()

Goal:
โ€ข See null values
โ€ข Understand distributions (mean, std, min, max)

3๏ธโƒฃ Check for Missing Values
df.isnull().sum()

๐Ÿ“Œ Fix options:
โ€ข df.fillna(0) โ€“ Fill missing values
โ€ข df.dropna() โ€“ Remove rows with nulls

4๏ธโƒฃ Unique Values Frequency Counts
df['Region'].value_counts()
df['Product'].unique()

Goal: Understand categorical features.

5๏ธโƒฃ Data Type Conversion (if needed)
df['Date'] = pd.to_datetime(df['Date'])
df['Amount'] = df['Amount'].astype(float)


6๏ธโƒฃ Detecting Duplicates Removing
df.duplicated().sum()
df.drop_duplicates(inplace=True)


7๏ธโƒฃ Univariate Analysis (1 Variable)
import seaborn as sns
import matplotlib.pyplot as plt

sns.histplot(df['Sales'])
sns.boxplot(y=df['Profit'])
plt.show()

Goal: View distribution and detect outliers.

8๏ธโƒฃ Bivariate Analysis (2 Variables)
sns.scatterplot(x='Sales', y='Profit', data=df)
sns.boxplot(x='Region', y='Sales', data=df)


9๏ธโƒฃ Correlation Analysis
sns.heatmap(df.corr(numeric_only=True), annot=True)

Goal: Identify relationships between numerical features.

๐Ÿ”Ÿ Grouped Aggregation
df.groupby('Region')['Revenue'].sum()
df.groupby(['Region', 'Category'])['Sales'].mean()

Goal: Segment data and compare.

1๏ธโƒฃ1๏ธโƒฃ Time Series Trends (If date present)
df.set_index('Date')['Sales'].resample('M').sum().plot()
plt.title("Monthly Sales Trend")


๐Ÿง  Key Questions to Ask During EDA:
โ€ข Are there missing or duplicate values?
โ€ข Which products or regions perform best?
โ€ข Are there seasonal trends in sales?
โ€ข Are there outliers or strange values?
โ€ข Which variables are strongly correlated?

๐ŸŽฏ Goal of EDA:
โ€ข Spot data quality issues
โ€ข Understand feature relationships
โ€ข Prepare for modeling or dashboarding

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โœ… SQL Functions Interview Questions with Answers ๐ŸŽฏ๐Ÿ“š

1๏ธโƒฃ Q: What is the difference between COUNT(*) and COUNT(column_name)?
A:
- COUNT(*) counts all rows, including those with NULLs.
- COUNT(column_name) counts only rows where the column is NOT NULL.

2๏ธโƒฃ Q: When would you use GROUP BY with aggregate functions?
A:
Use GROUP BY when you want to apply aggregate functions per group (e.g., department-wise total salary):
SELECT department, SUM(salary) FROM employees GROUP BY department;


3๏ธโƒฃ Q: What does the COALESCE() function do?
A:
COALESCE() returns the first non-null value from the list of arguments.
Example:
SELECT COALESCE(phone, 'N/A') FROM users;


4๏ธโƒฃ Q: How does the CASE statement work in SQL?
A:
CASE is used for conditional logic inside queries.
Example:
SELECT name,  
CASE
WHEN score >= 90 THEN 'A'
WHEN score >= 75 THEN 'B'
ELSE 'C'
END AS grade
FROM students;


5๏ธโƒฃ Q: Whatโ€™s the use of SUBSTRING() function?
A:
It extracts a part of a string.
Example:
SELECT SUBSTRING('DataScience', 1, 4); -- Output: Data


6๏ธโƒฃ Q: Whatโ€™s the output of LENGTH('SQL')?
A:
It returns the length of the string: 3

7๏ธโƒฃ Q: How do you find the number of days between two dates?
A:
Use DATEDIFF(end_date, start_date)
Example:
SELECT DATEDIFF('2026-01-10', '2026-01-05'); -- Output: 5


8๏ธโƒฃ Q: What does ROUND() do in SQL?
A:
It rounds a number to the specified decimal places.
Example:
SELECT ROUND(3.456, 2); -- Output: 3.46


๐Ÿ’ก Pro Tip: Always mention real use cases when answering โ€” it shows practical understanding.

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1๏ธโƒฃ What does the following code print?

print("Hello, Python")
Anonymous Quiz
14%
A. Hello Python
73%
B. Hello, Python
9%
C. "Hello, Python"
4%
D. Syntax Error
โค11
2๏ธโƒฃ Which of these is a valid variable name in Python?
Anonymous Quiz
10%
A. 1name
80%
B. name_1
4%
C. name-1
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3๏ธโƒฃ What is the output of this code?

print(10 // 3)
Anonymous Quiz
50%
A. 3.33
38%
B. 3
3%
C. 4
9%
D. 3.0
โค8๐Ÿ”ฅ2
Which operator is used for string repetition?
Anonymous Quiz
21%
A. +
55%
B. *
17%
C. &
7%
D. %
โค7
What will this code output?*

print("Hi " * 2)
Anonymous Quiz
39%
A. HiHi
10%
B. Hi 2
42%
C. Hi Hi
9%
D. Error
โค6
What is the correct way to check the type of a variable x?
Anonymous Quiz
21%
A. typeof(x)
13%
B. checktype(x)
56%
C. type(x)
10%
D. x.type()
โค7๐Ÿ‘4๐Ÿ‘Ž2
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