Data Science tries to answer one of the following questions:
- Classification -> “Is it A or B?”
- Clustering -> “Are there groups which belong together?”
- Regression -> “How will it develop in the future?”
- Association -> “What is happening very often together?”
There are two ways to tackle these problem domains with machine learning:
- Supervised Learning
- Unsupervised Learning
You have training and test data with labels. Labels tell You to which e.g. class a certain data item belongs. Image you have images of pets and the labels are the name of the pets.
Your data doesn’t have labels. Your algorithm e.g. k-means clustering need to figure out a structure given only the data
Sometimes Python gives You a hard time when You deploy code to a server after you changed directory structures or simply moved files.
With the following command You can remove the pyc files in the working directory and subdirectories:
find . -name \*.pyc -delete
The Essence of Machine Learning
- A pattern exists
- The pattern cannot be described mathematically
- We have data on this problem
This episode is about the basic statements needed to create, read, update and delete data in a database system.
Let’s assume we work as a data scientist for Knight Industries. We want to help the Foundation of Law and Government to keep track of our operatives.
We decide to use a classic relational database management system or RDBMS. In order to explore Database Management Systems we can either install one locally or we can use an online tool like SQLFiddle.
To interact with RDBMS we use SQL – the Structured Query Language.
As the name says SQL (speak either S-Q-L or Sequel) is used to write structured queries. Think of “conversations” when You think of “queries”.
So, let’s fire up SQLFiddle. Continue reading “SQL-Basics: Create – Read – Update – Delete”
Sometimes your RDBMS does not allow You certain changes like updating a table without using a WHERE that uses a key column.
When You are really sure what You want to do:
SET SQL_SAFE_UPDATES = 0;
Sometimes You screw up your database design and you have redundancies i.e. your database is not normalized. If You want to correct that: Subqueries for the rescue! Continue reading “SQL-Basics – Subqueries: Update column with values from another column”
You can comment your queries with
-- This is a comment in SQL
SELECT * FROM my_table -- WHERE id = 1