Jitter text/labels with position_stack

Question

Consider the following data.frame and chart:

library(ggplot2)
library(scales)
df <- data.frame(L=rep(LETTERS[1:2],each=4),
                 l=rep(letters[1:4],2),
                 val=c(96.5,1,2,0.5,48,0.7,0.3,51))
#   L l  val
# 1 A a 96.5
# 2 A b  1.0
# 3 A c  2.0
# 4 A d  0.5
# 5 B a 48.0
# 6 B b  0.7
# 7 B c  0.3
# 8 B d 51.0

ggplot(df,aes(x=L,y=val,fill=l)) +
  geom_bar(stat="identity") +
  geom_text(aes(label=percent(val/100)),position=position_stack(vjust =0.5))

Some labels are hard to read due to small values. I'd like to jitter those vertically. I'm aware of position_jitter but it doesn't seem compatible with a stacked bar chart.

Answer 1

We can create a new Position, position_jitter_stack().

 position_jitter_stack <- function(vjust = 1, reverse = FALSE, 
                                  jitter.width = 1, jitter.height = 1,
                                  jitter.seed = NULL, offset = NULL) {
  ggproto(NULL, PositionJitterStack, vjust = vjust, reverse = reverse, 
          jitter.width = jitter.width, jitter.height = jitter.height,
          jitter.seed = jitter.seed, offset = offset)
}

PositionJitterStack <- ggproto("PositionJitterStack", PositionStack,
  type = NULL,
  vjust = 1,
  fill = FALSE,
  reverse = FALSE,
  jitter.height = 1,
  jitter.width = 1,
  jitter.seed = NULL,
  offset = 1,

  setup_params = function(self, data) {
    list(
      var = self$var %||% ggplot2:::stack_var(data),
      fill = self$fill,
      vjust = self$vjust,
      reverse = self$reverse,
      jitter.height = self$jitter.height,
      jitter.width = self$jitter.width,
      jitter.seed = self$jitter.seed,
      offset = self$offset
    )
  },

  setup_data = function(self, data, params) {
    data <- PositionStack$setup_data(data, params)
    if (!is.null(params$offset)) {
      data$to_jitter <- sapply(seq(nrow(data)), function(i) {
        any(abs(data$y[-i] - data$y[i]) <= params$offset)
      })
    } else {
      data$to_jitter <- TRUE
      }
    data
  },

  compute_panel = function(data, params, scales) {
    data <- PositionStack$compute_panel(data, params, scales)

    jitter_df <- data.frame(width = params$jitter.width,
                            height = params$jitter.height)

    if (!is.null(params$jitter.seed)) jitter_df$seed = params$jitter.seed
    jitter_positions <- PositionJitter$compute_layer(
      data[data$to_jitter, c("x", "y")],
      jitter_df
    )

    data$x[data$to_jitter] <- jitter_positions$x
    data$y[data$to_jitter] <- jitter_positions$y

    data
  }
)

And plot it ...

ggplot(df,aes(x=L,y=val,fill=l)) +
  geom_bar(stat="identity") +
  geom_text(aes(label=percent(val/100)),
            position = position_jitter_stack(vjust =0.5,
             jitter.height = 0.1,
             jitter.width =  0.3, offset = 1))

Alternatively, we could write a very simple repel function.

library(rlang)

position_stack_repel <- function(vjust = 1, reverse = FALSE, 
                                 offset = 1) {
  ggproto(NULL, PositionStackRepel, vjust = vjust, reverse = reverse,
          offset = offset)
}

PositionStackRepel <- ggproto("PositionStackRepel", PositionStack,
  type = NULL,
  vjust = 1,
  fill = FALSE,
  reverse = FALSE,
  offset = 1,

  setup_params = function(self, data) {
    list(
      var = self$var %||% ggplot2:::stack_var(data),
      fill = self$fill,
      vjust = self$vjust,
      reverse = self$reverse,
      offset = self$offset
    )
  },

  setup_data = function(self, data, params) {
    data <- PositionStack$setup_data(data, params)
    data <- data[order(data$x), ]
    data$to_repel <- unlist(by(data, data$x, function(x) {
      sapply(seq(nrow(x)), function(i) {
        (x$y[i]) / sum(x$y) < 0.1 & (
          (if (i != 1) (x$y[i-1] / sum(x$y)) < 0.1 else FALSE) | (
            if (i != nrow(x)) (x$y[i+1] / sum(x$y)) < 0.1 else FALSE))
      })
    }))
    data
  },

  compute_panel = function(data, params, scales) {
    data <- PositionStack$compute_panel(data, params, scales)
    data[data$to_repel, "x"] <- unlist(
      by(data[data$to_repel, ], data[data$to_repel, ]$x, 
         function(x) seq(x$x[1] - 0.3, x$x[1] + 0.3, length.out = nrow(x))))
    data
  }
)

Plot it:

ggplot(df,aes(x=L,y=val,fill=l)) +
  geom_bar(stat="identity") +
  geom_text(aes(label=percent(val/100)),
            position = position_stack_repel(vjust =0.5))