autoplot function for ggplot2 graphics

[wilsonfreitas]

Implement an autoplot function to create graphics with ggplot2.

This code has good examples on how it can be done.

https://github.com/wilsonfreitas/shinyapp-curvapre/blob/main/utils-functions.R

[wilsonfreitas]

The options to show forwardrates and interpolation could be handled as layers.