Custom forest plot with with ggplot2. Can't have multiple groups, CIs cross the lower limit

Question

I wrote a function to draw forest plots of CIs from regression results.

I feed to the function a data.frame with predictor label ($label), estimates ($coef), low and

Answer 1

You can get the results you want by creating two ggplot objects and putting them together via gridExtra::grid.draw.

Set up

library(ggplot2)
library(gridExtra)
library(grid)

regression_results <- 
  structure(list(label = structure(c(9L, 4L, 8L, 2L, 6L, 10L, 3L, 7L, 1L, 5L), 
                                   .Label = c("    - frattura esposta", "    - frattura esposta 2", "    - lembo di perone vs lembo corticoperiostale", "    - lembo di perone vs lembo corticoperiostale 2", "    - sesso maschile vs femminile", "    - sesso maschile vs femminile 2", "    - trauma bassa energia", "    - trauma bassa energia 2", "Tempo di guarigione 2:", "Tempo di guarigione:"), 
                                   class = "factor"), 
                 coef = c(NA, 0.812, 0.695, 1.4, 0.682, NA, 0.812, 0.695, 1.4, 0.682), 
                 ci.low = c(NA, 0.405, 0.31, 1.26, 0.0855, NA, 0.405, 0.31, 1.26, 0.0855), 
                 ci.high = c(NA, 1.82, 0.912, 2.94, 1.01, NA, 1.82, 0.912, 2.94, 1.01), 
                 style = structure(c(1L, 2L, 2L, 2L, 2L, 1L, 2L, 2L, 2L, 2L), 
                                   .Label = c("bold", "plain"), class = "factor")), 
            .Names = c("label", "coef", "ci.low", "ci.high", "style"), 
            class = "data.frame", 
            row.names = c(NA, -10L))

# Set a y-axis value for each label
regression_results$yval <- seq(nrow(regression_results), 1, by = -1)

Build a forest plot

# Forest plot
forest_plot <- 
  ggplot(regression_results) + 
    theme_bw() + 
    aes(x = coef, xmin = ci.low, xmax = ci.high, y = yval) + 
    geom_point() + 
    geom_errorbarh(height = 0.2, color = 'red') + 
    geom_vline(xintercept = 1) + 
    theme(
          axis.text.y = element_blank(),
          axis.title.y = element_blank(),
          axis.ticks.y = element_blank(),
          panel.grid.major.y = element_blank(), 
          panel.grid.minor.y = element_blank(), 
          panel.border = element_blank() 
          )  +
    ylim(0, 10) + 
    xlab("Odds Ratio")

build a plot of labels

# labels, could be extended to show more information
table_plot <-
  ggplot(regression_results) + 
    theme_bw() + 
    aes(y = yval) + 
    geom_text(aes(label = gsub("\\s2", "", label), x = 0), hjust = 0) + 
    theme(
          axis.text = element_blank(),
          axis.title = element_blank(),
          axis.ticks = element_blank(),
          panel.grid = element_blank(),
          panel.border = element_blank() 
          ) + 
    xlim(0, 6) +
    ylim(0, 10)

Produce the Plot

# build the plot
png(filename = "so-example.png", width = 8, height = 6, units = "in", res = 300)

grid.draw(gridExtra:::cbind_gtable(ggplotGrob(table_plot), ggplotGrob(forest_plot), size = "last"))

dev.off()