Use the tapply() function to calculate the average value of PM2.5 for each day in 2023.

(HINT: see the tapply() function example discussed in Topic 7 Practice Exercises)

Copy your R code below:

Have a look at the first 12 rows of the data frame pm2.5_hourly.

What

is the average value of PM2.5 on 1 Jan 2023?

(Report to 2 decimal places)

HINT: Use code and indexing to avoid rounding error. Do not type individual values in manually.

There are some negative values recorded for the

PM2.5 readings. How many of them?

If we only keep those positive values recorded for the PM2.5 readings, what will be the sample average?

(Report to 2 decimal places)

What is the R code to display the contents of

the second row of

What is the number of columns of the data frame pm2.5_2023_cbd?

The PM2.5 readings are stored in the column named value. What is the sample average of the PM2.5 readings recorded at the Melbourne CBD site in 2023?

(Report to 2 decimal places)

What will the following code display?

> head(pm2.5_2023_cbd$value)

What is the R code to display the element in row 100,

column 7 of