# Time series

> A list of measurements of the same thing, taken one after another in time.

- Level: Intermediate
- Topics: Data
- URL: https://tidbit.legios.com.ar/time-series/
- In Spanish: [Serie temporal](https://tidbit.legios.com.ar/es/time-series/)

A **time series** is a sequence of values of the same quantity recorded at successive moments: the temperature every hour, a stock price every second, a website's visits per day, a server's CPU use every ten seconds. What makes it special is that the order matters. Each point only makes sense next to the ones before and after it.

Analysts look for a few typical shapes in a time series. The **trend** is the long-term direction (slowly going up). **Seasonality** is a pattern that repeats on a calendar (more ice cream sold every summer, more traffic every Monday morning). And then there is noise: the random wiggle left over. Separating these is the basis of forecasting, from predicting next month's sales to planning how many servers a holiday will need.

Because this kind of data arrives constantly and is almost always read by time range, there are databases built just for it, called **time-series databases**, like InfluxDB, TimescaleDB or Amazon Timestream. They compress the data well and make questions like "average per minute over the last 24 hours" very fast. Monitoring tools for servers and IoT devices are built on top of them.

## An analogy

A child's height marked on the kitchen door frame every birthday. Each mark alone is just a number; together, in order, they show a trend, the growth spurts and roughly where the next mark will land.

## Keep in mind

- Values of one thing measured in time order; the order carries the meaning.
- Trend, seasonality and noise are the three parts analysts try to separate.
- The basis of forecasting: sales, demand, traffic, energy use.
- Time-series databases store this kind of data and query it by time range quickly.

## Go deeper

- [Time series on Wikipedia](https://en.wikipedia.org/wiki/Time_series)
- [Time series database on Wikipedia](https://en.wikipedia.org/wiki/Time_series_database)

## Related terms

- [Website](https://tidbit.legios.com.ar/website/): A set of web pages under one address, stored on a server and opened in a browser.
- [Server](https://tidbit.legios.com.ar/server/): A computer whose job is to answer requests from other computers, all day, every day.
- [CPU](https://tidbit.legios.com.ar/cpu/): The chip that runs your programs, one instruction after another, very fast.
- [Forecasting](https://tidbit.legios.com.ar/forecasting/): Using past data to estimate future numbers, with an honest range around the guess.
- [Database](https://tidbit.legios.com.ar/database/): An organized store of data that programs can search and update safely.
- [Amazon](https://tidbit.legios.com.ar/amazon/): An online store with its own delivery network, and the company that runs AWS.
- [Internet of things](https://tidbit.legios.com.ar/internet-of-things/): Everyday objects with sensors and a network connection: thermostats, meters, doorbells.