Can't add a probability-curve on the histogram

Question

I'm trying do display multiple histograms with one plot with the lattice-package.

That's my code so far:

histogram(~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8 + X9 + X10, data=mydata, 
      type = "density",layout=c(5,2),
      panel=function(x, ...) {
        panel.histogram(x, ...)
        panel.mathdensity(dmath=dnorm, col="black",
                          args=list(mean=mean(x), sd=sd(x)), ...)
      })

The problem is, that it won't plot the probability-curve. It doesn't give me an error back, so the code looks good, I think.

I also tried it with only one variable and it didn't work either:

histogram(~ X1, data=mydata, 
  type = "density",layout=c(5,2),
  panel=function(x, ...) {
    panel.histogram(x, ...)
    panel.mathdensity(dmath=dnorm, col="black",
                      args=list(mean=mean(x), sd=sd(x)), ...)
  })

Does anyone see an error in my code? Or could be something wrong in my data?

I'm glad for any advice!

Answer 1

Could it be that your data contain missing values?

# Create example data (no missings)
mydata <- data.frame(X1 = rpois(1000, 12), X2 = rnorm(1000, 12, sqrt(12)))

# Create some missing (NA) entries
mydata2 <- mydata
mydata2[sample(seq_len(nrow(mydata2)), 10), 1] <- NA

Using the above mydata2 object in the histogram function produces no density plot for X1, since mean and sd return NA. Adding na.rm = TRUE to both those functions will return values that panel.mathdensity can use:

histogram(~ X1 + X2, data=mydata2, 
      type = "density",layout=c(1,2),
      panel=function(x, ...) {
        panel.histogram(x, ...)
        panel.mathdensity(dmath=dnorm, col="black",
# Add na.rm = TRUE to mean() and sd()
                          args=list(mean=mean(x, na.rm = TRUE),
                                    sd=sd(x, na.rm = TRUE)), ...)
      })