Exploratory Data Analysis - A Comprehensive Guide to EDA.pdf

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Exploratory Data Analysis - A Comprehensive Guide to
EDA
leewayhertz.com/what-is-exploratory-data-analysis
In today’s data-driven world, the ability to effectively analyze data is a key factor in the
success of many enterprises. By leveraging data analysis tools and techniques, businesses
can gain insights, identify trends, and confidently make informed decisions based on their
data, improving efficiency and gaining an edge in the highly competitive business landscape.
Exploratory data analysis (EDA), which is a preliminary method used for interpreting data
before undertaking any formal modeling or hypothesis testing, is one of the most crucial
procedures involved in data analysis.
Exploratory Data Analysis is the process of detailing the key features of a dataset, frequently
employing visual techniques. It entails exploring and analyzing data to comprehend its
underlying patterns, connections and trends. EDA is important because it helps identify any
issues or anomalies in the data that could affect the reliability of the subsequent analysis.
Many industries benefit from EDA, including finance, healthcare, retail, and marketing, since
it serves as a foundation for data analysis, pinpoints potential shortcomings in the data, and
provides insightful analysis of customer behavior, market trends and business performance.
In data analysis, EDA can assist data analysts in identifying missing or incomplete data,
outliers and inconsistencies that can impact the statistical analysis of data. Conducting an
EDA can also help determine which variables are crucial to explaining the outcome variable

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and which ones can be excluded. Hence, EDA often serves as the first step in developing a
data model because it provides insights into the characteristics of the data.
In this article, we will explore EDA and its importance, process, tools, techniques and more.
What is Exploratory Data Analysis (EDA)?
Importance of EDA in data science
EDA methods and techniques
The EDA process
Types of EDA techniques
Visualization techniques in EDA
Exploratory data analysis tools
What is Exploratory Data Analysis (EDA)?
EDA or Exploratory Data Analysis is a method of examining and understanding data using
multiple techniques like visualization, summary statistics and data transformation to abstract
its core characteristics. EDA is done to get a sense of data and discover any potential
problems or issues which need to be addressed and is generally performed before formal
modeling or hypothesis testing. It aims to identify patterns, relationships, and trends in the
data and use this information to facilitate further analysis or decision-making. Data of
different types, including numerical, categorical and text, can be analyzed using EDA. It is
typically done before data analysis to identify and correct the errors in data and visualize the
key attributes of the data.

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Business
Question/
Problem
Data
Collection
& Storage
EDA
Data
Analysis
Data
Visualisation &
Storytelling
Business
Decision
LeewayHertz
EDA is a scientific approach to understanding the storing of data. Data scientists can use it
to discover patterns, spot anomalies, test hypotheses, or verify assumptions by manipulating
data sources effectively.
Importance of EDA in data science
Exploratory data analysis is an important phase in the data science process because it
enables data scientists to comprehend the data they are working with on a deeper level. Let
us find out why EDA is important in data science by defining its objectives:
1. Conducting an EDA can confirm if the collected data is practicable in the context of the
business problem at hand. If not, the data or the strategy adopted by the data analysts
needs to be changed.
2. It can reveal and resolve data quality issues, like duplicates, missing data, incorrect
values and data types and anomalies.
3. Exploratory data analysis plays a vital role in extracting meaningful insights from data
by revealing key statistical measures such as mean, median, and standard deviation.

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4. Oftentimes, some values deviate significantly from the standard set of values; these
are anomalies that must be verified before the data is analyzed. If unchecked, they can
create havoc in the analysis, leading to miscalculations. As such, one of the objectives
of EDA is to locate outliers and anomalies in the data.
5. EDA unveils the behavior of variables when clubbed together, assisting data scientists
in finding patterns, correlations, and interactions between these variables by visualizing
and analyzing the data. This information is helpful in creating AI models.
6. EDA helps find and drop unwanted columns and derive new variables. It can, thus,
assist in determining which features are most crucial for forecasting the target variable,
assisting in the choice of features to be included in modeling.
7. Based on the characteristics of the data, EDA can assist in identifying appropriate
modeling techniques.
EDA methods and techniques
Some of the common techniques and methods used in Exploratory Data Analysis include the
following:
Data visualization
Data visualization involves generating visual representations of the data using graphs,
charts, and other graphical techniques. Data visualization enables a quick and easy
understanding of patterns and relationships within data. Visualization techniques include
scatter plots, histograms, heatmaps and box plots.
Correlation analysis
Using correlation analysis, one can analyze the relationships between pairs of variables to
identify any correlations or dependencies between them. Correlation analysis helps in
feature selection and in building predictive models. Common correlation techniques include
Pearson’s correlation coefficient, Spearman’s rank correlation coefficient and Kendall’s tau
correlation coefficient.
Dimensionality reduction
In dimensionality reduction, techniques like principal component analysis (PCA) and linear
discriminant analysis (LDA) are used to decrease the number of variables in the data while
keeping as many details as possible.
Descriptive statistics
It involves calculating summary statistics such as mean, median, mode, standard deviation
and variance to gain insights into the distribution of data. The mean is the average value of
the data set and provides an idea of the central tendency of the data. The median is the mid-

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value in a sorted list of values and provides another measure of central tendency. The mode
is the most common value in the data set.
Clustering
Clustering techniques such as K-means clustering, hierarchical clustering, and DBSCAN
clustering help identify patterns and relationships within a dataset by grouping similar data
points together based on their characteristics.
Outlier detection
Outliers are data points that vary or deviate significantly from the rest of the data and can
have a crucial impact on the accuracy of models. Identifying and removing outliers from data
using methods like Z-score, interquartile range (IQR) and box plots method can help improve
the data quality and the models’ accuracy.
The EDA process
Conducting EDA requires expertise in multiple tools and programming languages. In the
example below, we would perform EDA using Python on the open-source web application,
Jupyter Notebook.
The EDA process can be summed up in three steps, which are:
1. Understanding the data
2. Cleaning the data
3. Analysis of the relationship between variables
Let us understand the process of Exploratory Data Analysis (EDA) step-by-step:
Understanding the data
Import necessary libraries
The first step is to import the required libraries. In this code block, the Pandas library is used
to read and manipulate data and the Pandas-profiling library is used for EDA. The datasets
module from the scikit-learn library is used to load the Iris dataset.
import pandas as pd
import pandas_profiling
from sklearn import datasets
Loading the dataset

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Next, we have to load the dataset. Here, we will be using the multivariate dataset named the
Iris dataset.
iris = datasets.load_iris()
Converting to Pandas DataFrame
The scikit-learn dataset is loaded as a Bunch object, similar to a dictionary. To use this
dataset with Pandas, we must convert it to a Pandas DataFrame.
iris_data = pd.DataFrame(iris.data, columns=iris.feature_names)
iris_data['target'] = iris['target']
Checking data attributes
It is always a good approach to check the attributes of the data, like its shape or the number
of rows and columns in the dataset. To check the shape of the data, run the following code:
iris_data.shape
To check the column names of the DataFrame, we use the columns attribute.
iris_data.columns
If your dataset is big, you can view the first few records of the DataFrame by running the
below code:
iris_data.head()
Cleaning the data
Once you are done with scanning the attributes of the data, you can make any necessary
modifications in the dataset, like changing the name of the columns or the raws. Remember
not to change the dataset’s variables, which can significantly impact the final result.
Check for null values
To clean the data, first, you must check for any null values in the variables. If any of the
variables in a dataset have null values, it can affect the analysis results. If your dataset has
missing data, handle them through approaches like imputation, deletion of observations or
variables, or using models that can handle missing data.
Dropping the redundant data and removing outliers
Next, if you find any redundant data in your dataset that does not add value to the output,
you can also remove them from the table. All the columns and rows are important in the iris
dataset we have taken. So we would not be dropping the data. In this step, we must also find

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any outliers in the data.
Analysis of the relationship between variables
The final step in the process of EDA is to analyze the relationship between variables. It
involves the following:
Correlation analysis: The analyst computes the correlation matrix between variables
to identify which variables are strongly correlated with each other.
Visualization: The data analyst creates visualizations to explore the relationship
between variables. This includes scatter plots, heatmaps, etc.
Hypothesis testing: The analyst performs statistical tests to test hypotheses about the
relationship between variables.
Run the following code to generate a report that includes various relationship analyses
between variables.
pandas_profiling.ProfileReport(iris_data)
You can view the output of the above code from this Github repository.
Types of EDA techniques
Several types of exploratory data analysis techniques can be used to gain insights into data.
Some common types of EDA include:
Univariate non-graphical
Univariate non-graphical exploratory data analysis is a simple yet fundamental method for
examining information that includes utilizing only one variable to analyze the data. Univariate
non-graphical EDA focuses on figuring out the underlying distribution or pattern in the data
and mentions objective facts about the population. This procedure includes the examination
of the attributes of the population distribution, including spread, central tendency, skewness
and kurtosis.
An average or middle value of a distribution is called the central tendency. A common
measure of central tendency is the mean, followed by the median and mode. As a
measure of central tendency, the median may be preferred if the distribution is skewed
or concerns are raised about outliers.
Spread shows how far off the information values are from the central tendency. The
standard deviation and variance are two valuable proportions of the spread. The
variance is the mean of the square of the individual deviations, and the standard
deviation is the foundation of the variance.

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Skewness and kurtosis are two more helpful univariate descriptors of the distribution.
Skewness is a metric of the asymmetry of the distribution, while kurtosis is a proportion
of the peakedness of the distribution contrasted with an ordinary dispersion.
Outlier detection is also important in univariate non-graphical EDA, as outliers can
significantly impact the distribution and distort statistical analysis results.
Multivariate non-graphical
Multivariate non-graphical EDA is a technique used to explore the relationship between two
or more variables through cross-tabulation or statistics. It is useful for identifying patterns and
relationships between variables. This analysis is particularly useful when multiple variables
exist in a dataset, and you want to see how they relate.
Cross-tabulation is a helpful extension of tabulation for categorical data. Cross-tabulation is
preferable when there are two variables involved. To do this, create a two-way table with
column headings corresponding to the number of one variable and row headings
corresponding to the number of the other two variables. Next, fill the counts with all subjects
with the same pair of levels.
We produce statistics for quantitative variables individually for each level of each categorical
variable and one quantitative variable, and then we compare the statistics across all
categorical variables. The purpose of multivariate non-graphical EDA is to identify
relationships between variables and understand how they are related. Examining the
relationship between variables makes it possible to discover patterns and trends that may
not be immediately obvious from examining individual variables in isolation.
Univariate graphical
A univariate graphical EDA technique employs a variety of graphs to gain insight into a single
variable’s distribution. These graphical techniques enable us to gain a quick understanding
of shapes, central tendencies, spreads, modalities, skewnesses, and outliers of the data we
are studying. The following are some of the most commonly used univariate graphical EDA
techniques:
1. Histogram: This is one of the most basic graphs used in EDA. A histogram is a bar
plot that displays the frequency or proportion of cases in each of several intervals (bins)
of a variable’s values. The height of each bar represents the count or proportion of
observations that fall within each interval. Histograms provide an intuitive sense of the
shape and spread of the distribution, as well as any outliers.

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2. Stem-and-leaf plots: A stem-and-leaf plot is an alternative to a histogram that displays
each data value along with its magnitude. In a stem-and-leaf plot, each data value is
split into a stem and leaf, with the stem representing the leading digits and the leaf
representing the trailing digits. This type of plot provides a visual representation of the
data’s distribution and can highlight features such as symmetry and skewness.
3. Boxplots: Boxplots, also known as box-and-whisker plots, provide a visual summary of
the distribution’s central tendency, spread and outliers. The box in a boxplot represents
the data’s interquartile range (IQR), with the median line inside the box. The whiskers
extend from the box to the smallest and largest observations within 1.5 times the IQR
from the box. Data points outside of the whiskers are considered outliers.
4. Quantile-normal plots: A quantile-normal plot, also known as a Q-Q plot, assesses
the data distribution by comparing the observed values to the expected values from a
normal distribution. In a Q-Q plot, the observed data is plotted against the quantiles of
a normal distribution. The points should lie along a straight line if the data is normally
distributed. If the data deviates from normality, the plot will reveal any skewness,
kurtosis, or outliers.
Multivariate graphical
A multivariate graphical EDA displays relationships between two or more data sets using
graphics. When examining relationships between variables beyond two, this technique is
used to gain a more comprehensive understanding of the data. A grouped barplot is one of
the most commonly used multivariate graphical techniques, with each group representing
one level of one variable and each bar representing its amount.
Multivariate graphics can also be represented in scatterplots, run charts, heat maps,
multivariate charts, and bubble charts.
Scatterplots are graphical representations displaying the relationship between two
quantitative/numerical variables. It consists of plotting one variable on the x-axis and
another on the y-axis. On the plot, each point represents an observation. Scatterplots
make it possible to identify outliers or patterns in the data and the direction and
strength of the relationship between any two variables.
A run chart is a line graph that shows how data changes over time. It is a simple but
powerful tool for tracking changes and monitoring trends in data. Run charts can be
used to detect trends, cycles, or shifts in a process over time.
A multivariate chart illustrates the relationship between factors and responses. It is a
type of scatterplot that depicts relationships between several variables simultaneously.
A multivariate chart depicts the relationship between variables and identifies patterns or
clusters in the data.

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Bubble chart is a data visualization that displays multiple circles (bubbles) in a two-
dimensional plot. The size of each circle represents a value of a third variable. Bubble
charts are often used to compare data sets with three variables, as they provide an
easy way to visualize the relationships between these variables.
Visualization techniques in EDA
Scatterplot
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LeewayHertz
Visualization techniques play an essential role in EDA, enabling us to explore and
understand complex data structures and relationships visually. Some common visualization
techniques used in EDA are:
1. Histograms: Histograms are graphical representations that show the distribution of
numerical variables. They help understand the central tendency and spread of the data
by visualizing the frequency distribution.
2. Boxplots: A boxplot is a graph showing the distribution of a numerical variable. This
visualization technique helps identify any outliers and understand the spread of the
data by visualizing its quartiles.
3. Heatmaps: They are graphical representations of data in which colors represent
values. They are often used to display complex data sets, providing a quick and easy
way to visualize patterns and trends in large amounts of data.
4. Bar charts: A bar chart is a graph that shows the distribution of a categorical variable.
It is used to visualize the frequency distribution of the data, which helps to understand
the relative frequency of each category.

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5. Line charts: A line chart is a graph that shows the trend of a numerical variable over
time. It is used to visualize the changes in the data over time and to identify any
patterns or trends.
6. Pie charts: Pie charts are a graph that showcases the proportion of a categorical
variable. It is used to visualize each category’s relative proportion and understand the
data distribution.
Exploratory data analysis tools
Spreadsheet software
Due to its simplicity, familiar interface and basic statistical analysis capabilities, spreadsheet
software such as Microsoft Excel, Google Sheets, or LibreOffice Calc is commonly used for
EDA. Using them, users can sort, filter, manipulate data and perform basic statistical
analysis, like calculating the mean, median and standard deviation.
Statistical software
Specialized statistical software such as R or Python and their various libraries and packages
offer more advanced statistical analysis tools, including regression analysis, hypothesis
testing, and time series analysis. This software allows users to write customized functions
and perform complex statistical analyses on large datasets.
Data visualization software
Visualization software like Tableau, Power BI, or QlikView enables users to create interactive
and dynamic data visualizations. These tools help users to identify patterns and relationships
in the data, allowing for more informed decision-making. They also offer various types of
charts and graphs, as well as the ability to create dashboards and reports. The software
allows data to be easily shared and published, making it useful for collaborative projects or
presentations.
Programming languages
Programming languages such as R, Python, Julia and MATLAB offer powerful numerical
computing capabilities and provide access to various statistical analysis tools. These
languages can be used to write customized functions for specific analysis needs and are
particularly useful when working with large datasets. They also enable the automation of
repetitive tasks, besides bringing flexibility in data handling and manipulation.
Business Intelligence (BI) tools

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BI tools like SAP BusinessObjects, IBM Cognos or Oracle BI offer a range of functionalities,
including data exploration, dashboards and reports. They allow users to visualize and
analyze data from various sources, including databases and spreadsheets. They provide
data preparation tools and quality management tools that can be used in business settings to
help organizations make data-driven decisions.
Data mining tools
Data mining tools such as KNIME, RapidMiner or Weka provide a range of functionalities,
including data preprocessing, clustering, classification and association rule mining. These
tools are particularly useful for identifying patterns and relationships in large datasets and
building predictive models. Data mining tools are used in various industries, including
finance, healthcare and retail.
Cloud-based tools
Cloud-based platforms such as Google Cloud, Amazon Web Services (AWS) and Microsoft
Azure offer a range of tools and services for data analysis. They provide a scalable and
flexible infrastructure for storing and processing data and offer a range of data analysis and
visualization tools. Cloud-based tools are particularly useful for working with large and
complex datasets, as they offer high-performance computing resources and the ability to
scale up or down depending on the project’s needs.
Text analytics tools
Text analytics tools like RapidMiner and SAS Text Analytics are used to analyze unstructured
data, such as text documents or social media posts. They use natural language processing
(NLP) techniques to extract insights from text data, such as sentiment analysis, entity
recognition and topic modeling. Text analytics tools are used in a range of industries,
including marketing, customer service and political analysis.
Geographic Information System (GIS) tools
GIS tools such as ArcGIS and QGIS are used to analyze and visualize geospatial data. They
allow users to map data and perform spatial analysis, such as identifying patterns and trends
in geographical data or performing spatial queries. GIS tools are used in a range of
industries, including urban planning, environmental management and transportation.
Endnote
Exploratory data analysis, or EDA, is an essential step that must be conducted before
moving forward with data analysis. It helps data scientists and analysts to understand and
gain insights into the data they are working on. It helps discover missing or wrong data that
may lead to bias or fault in the final analysis. Analysts can guarantee that the data used for

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analysis is accurate and reliable by cleaning and preprocessing the data during the EDA
process. EDA methods can also facilitate feature selection, identifying the vital features to be
included in machine learning models and improving model performance. Overall, EDA allows
for detecting anomalies, patterns and relationships within the data, which can help
businesses make informed decisions and acquire a competitive edge in the fast-evolving
tech sphere.
Take data analysis to the next level! Contact our Data Scientists and Data Analysts to
perform a comprehensive Exploratory Data Analysis (EDA) and unlock valuable insights from
your data.

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