Exercise

# Rolling apply with a custom function

The `rollapply`

function from `zoo`

allows you to apply any summary function to a rolling window. A summary function takes multiple numbers as input and returns a single number, like `mean()`

, `max()`

, `sum()`

, etc.

Depending on the kind of data you have, you might need to write a function that combines multiple statistics, like in the example of our `find_range()`

function in the video exercise.

In this exercise, you'll create a brief function that 'manually' calculates the mean value of a range of numbers, and apply it to a rolling window.

The dataset you'll work with, `daily_temp`

, and the `zoo`

and `ggplot2`

packages, are loaded for you.

Instructions 1/3

## Question

The mean of a dataset is defined by the total of all observations, divided by the number of observations. What two R functions do you need to calculate the mean 'by hand'? The `daily_temp`

time series is available to you.

### Possible answers

`sum()`

and `max()`

`sum()`

and `length()`

`max()`

and `length()`