What Is a Time-Series?

Since this is a book about time-series data, we should start with a clarification of what we are talking about. In this section, we'll introduce time-series and their characteristics, and we'll go through different kinds of problems and types of analyses relevant to machine learning and statistics.

Many disciplines, such as finance, public administration, energy, retail, and healthcare, are dominated by time-series data. Large areas of micro- and macro-economics rely on applied statistics with an emphasis on time-series analyses and modeling. The following are examples of time-series data:

• Daily closing values of a stock index
• Number of weekly infections of a disease
• Weekly series of train accidents
• Rainfall per day
• Sensor data such as temperature measurements per hour
• Population growth per year
• Quarterly earnings of a company over a number of years

This is only to name but a few. Any data...