How to Self Learn Data Science in 2022
Updated: Apr 17, 2022
A Project-Based Approach to Get Started in Data Science
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As someone who don’t hold a degree in data science, I am truly passionate about this field and decided to experiment on building my own curriculum to self learn data science in spare time. I would like to share my experience and hope to bring some insights if you want to share the same journey.
Project based learning is a good starting point for people already have some technical background but also want to explore the building blocks of data science. A typical data science / machine learning project comprises a lifecycle - from defining the objectives, data preprocessing, exploratory data analysis, feature engineering, model implementation to model evaluation. Each phase requires different skillsets, mainly statistics, programming, SQL, data visualization, mathematics and business knowledge.
I highly recommend Kaggle as the platform to experiment with your data science projects. With plenty of interesting datasets and a cloud based programming environment, you can easily get data source, code and notebooks from Kaggle for free. As a reader/writer on Medium , I also recommend using the platform to gain data science knowledge from professionals and share your own project all at the same place.
Why Project Based Approach?
It is practical and gives us a sense of achievement that we are doing something real!
It highlights the rationale of learning each pieces of content. This goal-oriented approach provides a bird eye view of how each little pieces work together to form the big picture
It allow us to actively retrieve the information as we are learning. “Active Recall” is proven to significantly enhance information retention, compared to conventional learning mechanism which only requires passively consuming knowledge.
Let's break down the project lifecycle into following 5 steps and we will see how each step connects to various knowledge domain.
1.Business Problem & Data Science Solution
The first step of a data science project is to identify the business problem and define the objectives of an experiment design or model deployment.
Skillset - Business Knowledge
At this stage, it doesn’t need technicals skill yet but demands business understanding to identify the problem and define the objectives. First to understand the domain specific terminology appeared in the dataset, then to translate a business requirement to a technical solution. It requires years of experience in the field to build up your knowledge. I can only recommend some websites that increase your exposure to some business domains, for example Harvard Business Review, Hubspot, Investopedia, TechCrunch. Additionally, I recommend the book "Data Science for Business" as an integrated view of data science and business.
Skillset - Statistics (Experiment Design)
After defining the problem, then it is to frame it into a data science solution. This starts with the knowledge in Experiment Design such as hypothesis testing, sampling, bias / variances, different types of errors, overfitting / underfitting.
In the article "An Interactive Guide to Hypothesis Testing in Python", I introduced various type of statistical testing - t test, ANOVA, Chi Square test etc.
Machine Learning fundamentally can be considered as a hypothesis testing process, where we needs to search for a model in the hypothesis space that best fits our observed data, and allows us to make prediction to unobserved data.
Useful Resource:
2. Data Extraction & Data Preprocessing
The second step is to collect data from various sources and transform the raw data into digestible format.
Skillset - SQL
SQL is a powerful language for communicating with and extracting data from structured database.
Additionally, learning SQL also assists with framing a mental model that helps you to generate insights through data querying techniques, such as grouping, filtering, sorting, and joining. You will also find similar logics appearing in other languages, such as Pandas and SAS.
Useful Resources:
Skillset - Python (Pandas)
It is essential to get comfortable with a programing language. The simple syntax makes Python a relatively easy language to start with. Here is a great video tutorial if you are new to Python: Python for Beginners - Learn Python in 1 Hour.
After a basic understanding, it is worth spending some time to learn Pandas library. Pandas is almost unavoidable if you use python for data extraction. It transforms database into dataframe - a table like format that we are most familiar with.In the stage of data preprocessing, it is required to examine and address following data quality issues, and these can all be done using Pandas.
address missing data
transform inconsistent data type
remove duplicated value
Useful Resources:
3. Data Exploration & Feature Engineering
The third step is data exploration, also known as EDA (exploratory data analysis) which reveals hidden characteristics and pattern in a dataset. It usually involves data visualization techniques, and followed by feature engineering to transform data based on the results of exploration.
Skillset - Statistics (Descriptive Statistics)
Data exploration use descriptive statistics to summarize characteristics of the dataset
mean, median, mode
standard deviation, skewness
correlation, covariance
distribution
After a solid understanding of the dataset characteristics, it requires to apply the most appropriate feature engineering techniques accordingly. For instance, use log transformation for right-skewed data and clipping methods to deal with outliers. Here I list some common feature engineering techniques:
categorical encoding
scaling
imputation
feature selection
Useful Resource:
Skillset - Data Visualization
Combining statistics and data visualization allows us to understand the data through appropriate visual representation. Whether you prefer using visualization package such as seaborn or matplotlib in Python and ggplot2 in R; or visualization tools like Tableau and PowerBI, it’s essential to understand the use case of different chart types:
bar chart
histogram
box plot
heatmap
scatter plot
...
If interested, feel free to check out my articles on EDA and data visualization:
4. Model Implementation
After all of the preparation so far, it’s finally the time to dive deeper into machine learning algorithms.
Skillset - Machine Learning
scikit-learn is a powerful Python library that allows beginners to get started in machine learning easily. It offers plenty of built-in functions and we can implement a model using several lines of code. Although it has already done the hard work for us, it is still crucial to understanding how the algorithms operate behind the scene and be able to distinguish the best use case for each. Generally, machine learning algorithms are categorized into supervised learning and unsupervised learning. Below are some of the most popular algorithms:
Supervised Learning:
Neural Network
Support Vector Machine
Unsupervised Learning:
PCA
Dimension Reduction
I have created notebook and code snippet for machine learning algorithms. If you are interested, check it out:
Other Useful Resources:
Skillset - Math
Many starters including me may have the question of why we need to learn Math in data science. As a beginner, math knowledge mainly assists in understanding the underlying theory behind the algorithms.
Moving forward, when we no longer rely on built in libraries for building machine learning models, it allows us to develop and optimize advanced algorithms. Additionally, hyperparameter tuning also involves advanced math knowledge for searching the best model that minimize the cost function.
This is when more complicated math topics come into place:
calculus
linear algebra
optimization problem
gradient descent
searching algorithms
Useful Resources:
5. Model Evaluation
Skillset - Statistics (Inferential Statistics)
Inferential Statistics is particular useful when making model prediction and evaluating model performance. As opposed to descriptive statistics, inferential statistics focuses on generalizing the pattern observed in the sample data to a wider population. It provides evidence of which features have the high importance in making inference. Also it determines the model performance based on evaluation metrics.
For example, for classification problem where the output is discrete category, some common metrics are:
Confusion matrix
Type 1 error / Type 2 error
Accuracy
ROC / AUC
Whereas, for regression problem where the output is continuous numbers, some common metrics are:
R Squared
Root Mean Squared Error (RMSE), Mean Absolute Error (MAE), Mean Squared Error (MSE)
Useful Resources
Take-Home Message
It is a general guide that documents the learning journey I followed through, so I hope this can help some starters that are also passionate about data science and would like to invest their spare time exploring this field. Most topics I mentioned in the article are at surface level, and allows you to choose a field to dig deeper based on your own preference. If you find it helpful and would like to read more articles like this, please support by signing up Premium Membership.