How to avoid repeating code in a function to draw a density histogram and a simple histogram with ggplot2?

Question

I am trying to create a function that allows you to draw an histogram or a density histogram depending on your choice.

This is the function that I have:

library(ggplot2)
library(dplyr)

hist_function <- function(DF1, x = Variable1, fill_col = Variable2, x_axis = "x_axis", 
                          y_axis = "ylab", title_plot, var_name, bins=5, col_border="black", alpha=0.2, 
                          Density_Curve="TRUE", colour_curve="red", legend_title="title", lwd=1.2){
  
  if(Density_Curve == "TRUE"){
    p <- DF1 %>% 
      ggplot(aes(x)) +
      geom_histogram(aes(y=..density.., fill = fill_col), bins=bins, col=col_border, alpha=alpha) +
      geom_density(lwd = lwd, colour=colour_curve, show.legend = FALSE) +
      scale_x_continuous(breaks=pretty(x, n=10)) +
      xlab(x_axis) + 
      ylab(y_axis) +
      ggtitle(paste0(title_plot, var_name)) +
      guides(fill=guide_legend(title=legend_title)) +
      theme(strip.text.y = element_blank())
    
   }else{
    p <- DF1 %>%
      ggplot(aes(x)) +
      geom_histogram(aes(fill=fill_col), bins=bins, col=col_border, alpha=alpha) +
      scale_x_continuous(breaks=pretty(x, n=10)) +
      xlab(x_axis) +
      ylab(y_axis) +
      ggtitle(paste0(title_plot, var_name)) +
      guides(fill=guide_legend(title=legend_title)) +
      theme(strip.text.y = element_blank())
  }
  return(p)
}

mydf <- iris

Using the function:

# Draw a simple histogram

hist_function(DF1=mydf, x=mydf$Sepal.Length, fill_col = mydf$Species, var_name = "Sepal.Length",Density_Curve = "FALSE", x_axis = "Length", legend_title ="Species", y_axis ="Frequency", title_plot = "Histogram of ")

# Draw a density histogram

hist_function(DF1=mydf, x=mydf$Sepal.Length, fill_col = mydf$Species, var_name = "Sepal.Length", Density_Curve = "TRUE", x_axis = "Length", legend_title ="Species", y_axis ="Density",title_plot = "Distribution of ")

The function works perfectly fine, although I think that I am repeating a lot of code since most of the code to draw the plot is shared for both. The only difference is here:

#simple histogram
geom_histogram(aes(y=..density.., fill = fill_col), bins=bins, col=col_border, alpha=alpha) 
  geom_density(lwd = lwd, colour=colour_curve, show.legend = FALSE) 

VS

#density histogram
geom_histogram(aes(fill=fill_col), bins=bins, col=col_border, alpha=alpha) 

Does anybody have an idea about how to reduce the code?

Thanks in advance

Answer 1

Here the solution. Thanks for the idea @Limey!

library(ggplot2)
library(dplyr)

hist_function <- function(DF1, x = Variable1, x_axis = "x_axis", 
                          y_axis = "ylab", title_plot, var_name,
                          Density_Curve="TRUE", legend_title="title"){
  DF1 %>% 
      ggplot(aes(x)) +
      scale_x_continuous(breaks=pretty(x, n=10)) +
      xlab(x_axis) + 
      ylab(y_axis) +
      ggtitle(paste0(title_plot, var_name)) +
      guides(fill=guide_legend(title=legend_title)) +
      theme(strip.text.y = element_blank())
  
}

mydf <- iris

Density histogram

p= hist_function(DF1=mydf, x=mydf$Sepal.Length, var_name = "Sepal.Length", x_axis = "Length", 
                 legend_title ="Species", y_axis ="Density",title_plot = "Distribution of ")
p = p+geom_histogram(aes(y=..density.., fill = Species), bins=5, col="black", alpha=0.2) 
p = p + geom_density(lwd = 1.2, colour="red", show.legend = FALSE) 
p

Simple histogram

p2 = hist_function(DF1=mydf, x=mydf$Sepal.Length, var_name = "Sepal.Length", x_axis = "Length", 
              legend_title ="Species", y_axis ="Frequency", title_plot = "Histogram of ")
p2 = p2+ geom_histogram(aes(fill=Species), bins=5, col="black", alpha=0.2) 
p2