# Compute custom proportions with `stat_prop()`

    library(ggstats)
    library(ggplot2)

`stat_prop()` is a variation of `ggplot2::stat_count()` allowing to compute custom proportions according to the by aesthetic defining the denominator (i.e. all proportions for a same value of by will sum to 1). The by aesthetic should be a factor. Therefore, `stat_prop()` requires the by aesthetic and this by aesthetic should be a factor.

## Adding labels on a percent stacked bar plot

When using `position = "fill"` with `geom_bar()`, you can produce a percent stacked bar plot. However, the proportions corresponding to the y axis are not directly accessible using only `ggplot2`. With `stat_prop()`, you can easily add them on the plot.

In the following example, we indicated `stat = "prop"` to `ggplot2::geom_text()` to use `stat_prop()`, we defined the by aesthetic (here we want to compute the proportions separately for each value of x), and we also used `ggplot2::position_fill()` when calling `ggplot2::geom_text()`.

    d <- as.data.frame(Titanic)
    p <- ggplot(d) +
      aes(x = Class, fill = Survived, weight = Freq, by = Class) +
      geom_bar(position = "fill") +
      geom_text(stat = "prop", position = position_fill(.5))
    p

Note that `stat_prop()` has properly taken into account the weight aesthetic.

`stat_prop()` is also compatible with faceting. In that case, proportions are computed separately in each facet.

    p + facet_grid(cols = vars(Sex))

## Displaying proportions of the total

If you want to display proportions of the total, simply map the by aesthetic to `1`. Here an example using a stacked bar chart.

    ggplot(d) +
      aes(x = Class, fill = Survived, weight = Freq, by = 1) +
      geom_bar() +
      geom_text(
        aes(label = scales::percent(after_stat(prop), accuracy = 1)),
        stat = "prop",
        position = position_stack(.5)
      )

## A dodged bar plot to compare two distributions

A dodged bar plot could be used to compare two distributions.

    ggplot(d) +
      aes(x = Class, fill = Sex, weight = Freq, by = Sex) +
      geom_bar(position = "dodge")

On the previous graph, it is difficult to see if first class is over- or under-represented among women, due to the fact they were much more men on the boat. `stat_prop()` could be used to adjust the graph by displaying instead the proportion within each category (i.e. here the proportion by sex).

    ggplot(d) +
      aes(x = Class, fill = Sex, weight = Freq, by = Sex, y = after_stat(prop)) +
      geom_bar(stat = "prop", position = "dodge") +
      scale_y_continuous(labels = scales::percent)

The same example with labels:

    ggplot(d) +
      aes(x = Class, fill = Sex, weight = Freq, by = Sex, y = after_stat(prop)) +
      geom_bar(stat = "prop", position = "dodge") +
      scale_y_continuous(labels = scales::percent) +
      geom_text(
        mapping = aes(
          label = scales::percent(after_stat(prop), accuracy = .1),
          y = after_stat(0.01)
        ),
        vjust = "bottom",
        position = position_dodge(.9),
        stat = "prop"
      )

## Displaying unobserved levels

With the `complete` argument, it is possible to indicate an aesthetic for those statistics should be completed for unobserved values.

    d <- diamonds |>
      dplyr::filter(!(cut == "Ideal" & clarity == "I1")) |>
      dplyr::filter(!(cut == "Very Good" & clarity == "VS2")) |>
      dplyr::filter(!(cut == "Premium" & clarity == "IF"))
    p <- ggplot(d) +
      aes(x = clarity, fill = cut, by = clarity) +
      geom_bar(position = "fill")
    p +
      geom_text(
        stat = "prop",
        position = position_fill(.5)
      )

Adding `complete = "fill"` will generate “0.0%” labels where relevant.

    p +
      geom_text(
        stat = "prop",
        position = position_fill(.5),
        complete = "fill"
      )

## Using `geom_prop_bar()` and `geom_prop_text()`

The dedicated geometries `geom_prop_bar()` and `geom_prop_text()` could be used for quick and easy proportional bar plots. They use by default `stat_prop()` with relevant default values. For example, proportions are computed by x or y if the `by` aesthetic is not specified. It allows to generate a quick proportional bar plot.

    ggplot(diamonds) +
      aes(y = clarity, fill = cut) +
      geom_prop_bar() +
      geom_prop_text()

You can specify a `by` aesthetic. For example, to reproduce the comparison of the two distributions presented earlier.

    d <- as.data.frame(Titanic)
    ggplot(d) +
      aes(x = Class, fill = Sex, weight = Freq, by = Sex) +
      geom_prop_bar(position = "dodge") +
      geom_prop_text(
        position = position_dodge(width = .9),
        vjust = - 0.5
      ) +
      scale_y_continuous(labels = scales::percent)

You can also display counts instead of proportions.

    ggplot(diamonds) +
      aes(x = clarity, fill = cut) +
      geom_prop_bar(height = "count") +
      geom_prop_text(
        height = "count",
        labels = "count",
        labeller = scales::number
      )
    #> Warning in ggplot2::geom_bar(mapping = mapping, data = data, position =
    #> position, : Ignoring unknown parameters: `height`
    #> Warning in ggplot2::geom_text(mapping = mapping, data = data, position =
    #> position, : Ignoring unknown parameters: `height`, `labels`, and `labeller`