Error in ggplot(heart, aes(x = age)) : could not find function "ggplot"

This error message means that the function "ggplot" is not recognized by R.

The cause of this error message could be due to several reasons, including:

- The ggplot2 package is not installed in R. To install the package, you can run the command: `install.packages("ggplot2")`.

- The ggplot2 package is installed, but not loaded into R. To load the package, you can run the command: `library(ggplot2)`.

- There is a typo in the command you are trying to run. Double-check the spelling and syntax of your code to ensure that it is correct.

- The data frame you are using in the ggplot function is not defined or loaded into R. Make sure that you have loaded or created the data frame before using it in the ggplot function.