could not find function "describe.by"

The error message "could not find function 'describe.by'" indicates that R is unable to locate the function 'describe.by'. This error can occur if the package containing the function is not installed or if the package is not loaded into the current session.

To resolve this issue, you can try the following steps:

1. Make sure that you have installed the package that contains the function 'describe.by'. You can install the 'psych' package using the following command: `install.packages("psych")`

2. Load the 'psych' package into the current R session using the following command: `library(psych)`

3. Try using the 'describe.by' function again to see if the error has been resolved.

If these steps do not resolve the issue, you may need to check if the function is spelled correctly and if there are any typos in your code.