Error in stat_function for dnbinom

[Timothy Lau]

If I  have a histogram

x <- data.frame(x = rnorm(n = 100, mean = 1, sd = 1))

ggplot(data = x, mapping = aes(x = x)) + geom_histogram(binwidth = 0.5)

and I want to overlay a density plot I can use:

ggplot(data = x, mapping = aes(x = x)) + 

  geom_histogram(mapping = aes(y = ..density..), binwidth = 0.5) + 

  stat_function(fun = dnorm, args = list(mean = mean(x$x), sd = sd(x$x)), color = "black") +

  geom_vline(mapping = aes(xintercept = mean(x = x, na.rm = T)), color = "red", linetype = "dashed", size = 1)

​But this method undesirably changes my ​y-axis to the density. So I found that I can use:

​ggplot(data = x, aes(x = x)) +

  stat_bin(binwidth = 0.5, color = "black", fill = NA) +

  stat_function(fun = dnorm.count, args = list(mean = mean(x$x), sd = sd(x$x), n = nrow(x), binwidth = 0.5), color = "red") +

  geom_vline(mapping = aes(xintercept = mean(x = x, na.rm = T)), color = "red", linetype = "dashed", size = 1) +

  stat_bin(binwidth = 0.5, geom = "text", mapping = aes(label = ..count..), vjust = -0.5)

Which is okay, but when I try to do the same thing for a negative binomial distribution (instead of Gaussian as before):

dnbinom.count <- function(x, mu , size, log = FALSE, n = 1, binwidth = 1){

  n * binwidth * dnorm(x = x, mu = mu, size = size, log = log) 

}

y <- data.frame(y = rnbinom(n = 1000, mu = 5, size = 8))

ggplot(data = y, aes(x = y)) +

  stat_bin(binwidth = 1, color = "black", fill = NA) +

  stat_function(fun = dnbinom.count, args = list(mu = mean(y$y), size = sd(y$y)^2, n = nrow(y), binwidth = 1), color = "red") +

  geom_vline(mapping = aes(xintercept = mean(x = y, na.rm = T)), color = "red", linetype = "dashed", size = 1) +

  stat_bin(binwidth = 1, geom = "text", mapping = aes(label = ..count..), vjust = -0.5)

 I get the following error​:

Warning message:

Computation failed in `stat_function()`:

unused arguments (mu = mu, size = size) 

Can someone help me with this error? Or possibly suggest a simpler suggestion to viewing a density plot overlaid on my histogram that preserves my count y-axis.

Best,

Timothy

"The will to win means nothing without the will to prepare."

http://en.wikipedia.org/wiki/Juma_Ikangaa

[Loveland, Adam]

Shouldn’t your dnbinom.count function instead call dnbinom (and not dnorm)?

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