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Building a Factory

library(factory)

To build a function factory, begin by writing the function that you want to generalize (like a normal function). Here we’ll generalize a function to add a color scale to a ggplot using a custom palette.

my_scale_color <- function(discrete = TRUE, reverse = FALSE, ...) {
  my_palette <- c(
    "#772277", "#333388", "#1144aa", "#55aa11", 
    "#f40000", "#f47a00", "#ffe314"
  )
  if (reverse) {
    my_palette <- rev(my_palette)
  }
  pal <- colorRampPalette(my_palette, ...)
  
  if (discrete) {
    ggplot2::discrete_scale(
      aesthetics = "colour",
      scale_name = "my_color_scale", 
      palette = pal,
      ...
    )
  } else {
    ggplot2::scale_color_gradientn(colors = pal(256),)
  }
}

ggplot2::ggplot(mtcars) + 
  ggplot2::aes(x = mpg, y = cyl, color = factor(gear)) +
  ggplot2::geom_point() + 
  my_scale_color()

We could conceivably want to generalize this function to create a similar function, given a palette and (optionally) the name of the scale.

my_scale_color_generic <- function(discrete = TRUE, reverse = FALSE, ...) {
  my_palette <- this_palette
  if (reverse) {
    my_palette <- rev(my_palette)
  }
  pal <- colorRampPalette(my_palette, ...)
  
  if (discrete) {
    ggplot2::discrete_scale(
      aesthetics = "colour",
      scale_name = this_scale_name, 
      palette = pal,
      ...
    )
  } else {
    ggplot2::scale_color_gradientn(colors = pal(256),)
  }
}

We can use factory::build_factory to turn that function into a factory.

my_scale_color_factory <- build_factory(
  fun = my_scale_color_generic,
  this_palette,
  this_scale_name = "my_color_scale"
)

Using our factory with the values we started with should reproduce the original function.

my_scale_color_factory(
  this_palette = c(
    "#772277", "#333388", "#1144aa", "#55aa11", 
    "#f40000", "#f47a00", "#ffe314"
  )
)
#> function (discrete = TRUE, reverse = FALSE, ...) 
#> {
#>     my_palette <- c("#772277", "#333388", "#1144aa", "#55aa11", 
#>     "#f40000", "#f47a00", "#ffe314")
#>     if (reverse) {
#>         my_palette <- rev(my_palette)
#>     }
#>     pal <- colorRampPalette(my_palette, ...)
#>     if (discrete) {
#>         ggplot2::discrete_scale(aesthetics = "colour", scale_name = "my_color_scale", 
#>             palette = pal, ...)
#>     }
#>     else {
#>         ggplot2::scale_color_gradientn(colors = pal(256), )
#>     }
#> }

Note: If you use factory to build a factory in a package, we recommend that you copy/paste the resulting function definition into your package, rather than using the factory::build_factory call directly in your package. This will allow you to better comment your code, and will avoid build errors.

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.
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