Working with Dataframes Using pandas
6. Working with Dataframes Using pandas#
Data scientists work with data stored in tables. This chapter introduces
dataframes, one of the most widely used ways to represent data tables. We
also introduce pandas, the standard Python package for working with
dataframes. Here is an example of a dataframe that holds information about
popular dog breeds:
| grooming | food_cost | kids | size | |
|---|---|---|---|---|
| breed | ||||
| Labrador Retriever | weekly | 466.0 | high | medium |
| German Shepherd | weekly | 466.0 | medium | large |
| Beagle | daily | 324.0 | high | small |
| Golden Retriever | weekly | 466.0 | high | medium |
| Yorkshire Terrier | daily | 324.0 | low | small |
| Bulldog | weekly | 466.0 | medium | medium |
| Boxer | weekly | 466.0 | high | medium |
In a dataframe, each row represents a single record—in this case, a single dog breed. Each column represents a feature about the record—for example, the grooming column represents how often each dog breed needs to be groomed.
Dataframes have labels for both columns and rows. For instance, this dataframe has a column labeled grooming and a row labeled German Shepherd. The columns and rows of a dataframe are ordered—we can refer to the Labrador Retriever row as the first row of the dataframe.
Within a column, data have the same type. For instance, the the cost of food contains numbers, and the size of the dog consists of categories. But data types can be different within a row.
Because of these properties, dataframes enable all sorts of useful operations.
Note
Data scientists often find themselves working with people from different backgrounds who use different terms. For instance, computer scientists say that the columns of a dataframe represent features of the data, while statisticians call them variables instead.
Other times, people use the same term to refer to slightly different
ideas. Data types in a programming sense refers to how a computer stores
data internally. For instance, the size column has a string data type in
Python. But from a statistical point of view, the type of the size column is ordered categorical data (ordinal data). We talk more about this specific distinction in Exploratory Data Analysis.
In this chapter, we introduce common dataframe operations using
pandas. Data scientists use the pandas library when working with dataframes
in Python. First, we explain the main objects that pandas provides: the
DataFrame and Series classes. Then we show how to use pandas to
perform common data manipulation tasks, like slicing, filtering, sorting,
grouping, and joining.