Using stat_function() and geom_function()

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These are used to compute and draw a function as a continuous curve. For example - a standard normal curve can be drawn from the dnorm() function -

> library(ggplot2)
> ggplot() + 
+   xlim(-3, 3) + 
+   stat_function(fun = dnorm, geom = "polygon", fill = "#44adb7", color = "#1a4145") + 
+   theme_bw() + labs(title = "Standard Normal Curve")

To specify arguments of the function, use args -

> ggplot() + 
+   xlim(25, 55) + 
+   stat_function(fun = dnorm, args = list(mean = 40, sd = 3),
+                 geom = "polygon", fill = "#44adb7", color = "#1a4145") + 
+   theme_bw() + labs(title = "Normal Curve")

Adding multiple functions to the same plot -

> ggplot() + 
+   xlim(25, 65) + 
+   stat_function(fun = dnorm, args = list(mean = 40, sd = 3), 
+                 alpha = 0.5, aes(color = "Mean 40"),
+                 geom = "polygon", fill = "#44adb7", color = "#1a4145") + 
+   stat_function(fun = dnorm, args = list(mean = 50, sd = 3), 
+                 alpha = 0.5, aes(color = "Mean 50"),
+                 geom = "polygon", fill = "#04fda4", color = "#1a4145") + 
+   theme_bw() + labs(title = "Normal Curves")

Using geom_function() -

> ggplot() + 
+   xlim (-4, 4) +
+   geom_function(fun = dnorm, aes(colour = "Normal")) +
+   geom_function(fun = dt, args = list(df = 7), aes(colour = "t, df = 7")) +
+   theme_bw() + labs(title = "Normal and t Distribution", color=NULL) 

> ggplot() + 
+   xlim(25, 65) + 
+   geom_function(fun = dnorm, args = list(mean = 40, sd = 3), 
+                 aes(color = "Mean = 40")) + 
+   geom_function(fun = dnorm, args = list(mean = 50, sd = 3), 
+                 aes(color = "Mean = 50")) + 
+   theme_bw() + labs(title = "Normal Curves", color=NULL) 

Overlay a function over a plot -

> ggplot(data.frame(x = rnorm(100)), aes(x)) +
+   geom_density() +
+   geom_function(fun = dnorm, colour = "red") +
+   xlim(-4, 4)

Using a custom function -

> sigmoid <- function(x){ 1/(1+exp(-x)) }
> ggplot() +        
+   xlim(-10, 10) + 
+   stat_function(fun = sigmoid) +  # adding function
+   theme_bw() + labs(title = "Sigmoid Curve")

Another way to pass a custom function -

> ggplot() +        
+   xlim(-10, 10) + 
+   stat_function(fun = ~ 1/(1+exp(-.x)) ) + # Another way to specify the function
+   theme_bw() + labs(title = "Sigmoid Curve")