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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
27. Summary for a filtered data frame
Summary

## Instruction

Nice! You can also use summary on filtered data frames. For example, if Versico's management wants to examine the summary statistics of German cities with populations greater than 1 million, we can call the summary() function on a filtered data frame like this:

summary(cities[cities$country == "Germany" & cities$population > 1000000, ])

R will return the following output:

   country          ...    latitude      ...
Length:7           ...  Min.   :48.13   ...
Class :character   ...  1st Qu.:49.14   ...
Mode  :character   ...  Median :50.10   ...
Mean   :50.58   ...
3rd Qu.:51.99   ...
Max.   :53.55   ...


If you take a look at the population column, you will notice quite different results than those presented for the whole data frame — the minimum value is greater than 1 million, and the maximum is greater than 3 million. Of course, this is because our filtered subset only contains German cities whose populations exceed 1 million inhabitants.

## Exercise

Display summary statistics for countries in WESTERN EUROPE that have more than 50 million inhabitants. Call the summary() function on the filtered data frame.

### Stuck? Here's a hint!

You have to apply the following filtering before:

countries[countries$region == "WESTERN EUROPE" & countries$population > 50000000, ]