Introduction to data frames
Data frame structure
Accessing columns in a data frame
Accessing rows of a data frame
Accessing rows and columns combined in a data frame
Data frame analysis
28. Analyzing filtered data frames
Summary

## Instruction

Great! Of course, you can apply all data frame analysis functions to filtered data frames. Let's try this in an exercise.

## Exercise

How many countries have more than 50 million people? Use the countries data frame to extract the rows that match this condition, and use them in your analysis.

### Stuck? Here's a hint!

Use nrow(), and pass in a data frame that is a subset of the original table. You can do so with the following code:

countries\$population > 50000000