plot histogram and pdf in same plot for poisson

Question

I have a dataset which i need to analyse with poisson regression. I try to plot the histrogram of the respons in the same plot as the pdf but i don't find how..

i plot my histogram with the following code:

library(lattice) 
tot <- mydata[, 1] 
histogram(tot) 

and get a nice histogram. To add the pdf i've tried some codes lie the one below:

xlines <-seq(min(tot),max(tot),length.out=100)  
lines(x = xlines,y=dpois(xlines,21))

I've tried a few other codes as well but can't find one that works...
Somebody has some suggestions?

Answer 1

You can start working on this code:

library(lattice) 
set.seed(1)
tot <- rpois(100,21)
xlines <- seq(min(tot),max(tot),by=1)
histogram(tot, type="density", 
  panel=function(x, ...){
    panel.histogram(x,...)
    panel.lines(x = xlines, y=dpois(xlines,21), lwd=2, col="red")
  }
)