Save file as "generate_dataset.R" to use with "inverse_function.R". This specific script was used in wordpress post in [add link]

inverse_example_dataset.R

# Example of inverse function
# Generating x-axis, pdf and cdf numeric values.

# last modifyed: 29/04/2016

library(ggplot2)
library(tibble)
library(tidyr)


# Mathematical function ---------------------------------------------------

pdf_example <- function(x){
  flag <- F
  if(x >= -4 & x <= -1) flag <- T
  if(x >= 1  & x <=  4) flag <- T
  
  if(flag)
    -5 * (x^2 - 1) * (x^2 - 16) / 1044
  else
    0
}



# Create x-axis, pdf and cdf values  --------------------------------------


n <- 5000
dataset <- data_frame( x = seq(-5, 5, 10/n ))
dataset$pdf  <- sapply(X = unlist(dataset$x), FUN = pdf_example)


aux <- 0
freq_acum <- numeric()
for(i in 1:(n+1)){
  freq_acum[i] <- dataset$pdf[i] + aux
  aux <- dataset$pdf[i] + aux 
}
dataset$cdf <- freq_acum / sum(dataset$pdf)
dataset <- gather(dataset, dens, freq, -x)


# Plot the results --------------------------------------------------------

g <- ggplot(dataset, aes(x, freq, group = dens)) + theme_minimal() +
  geom_ribbon(aes(ymin = 0, ymax = freq, fill = dens), alpha =0.6, color = "black") + 
  xlab("value") + ylab("frequency") + scale_fill_brewer() +
  ggtitle("Dataset generated - {x-axis, pdf, cdf}")

# g + geom_segment(aes(x = 0, xend = 0, y = 0, yend = 1/2), color = "dark blue", size = 0.75) +
#   geom_segment(aes(x = -5, xend = 0, y = 1/2, yend = 1/2), color = "dark blue", size = 0.75)