R: changing x-axis tick mark labels in forestplot

Question

library(forestplot)
# Cochrane data from the 'rmeta'-package
cochrane_from_rmeta <- 
  structure(list(
    mean  = c(NA, NA, 0.578, 0.165, 0.246, 0.700, 0.348, 0.139, 1.017, NA, 0.531), 
    lower = c(NA, NA, 0.372, 0.018, 0.072, 0.333, 0.083, 0.016, 0.365, NA, 0.386),
    upper = c(NA, NA, 0.898, 1.517, 0.833, 1.474, 1.455, 1.209, 2.831, NA, 0.731)),
    .Names = c("mean", "lower", "upper"), 
    row.names = c(NA, -11L), 
    class = "data.frame")

tabletext<-cbind(
  c("", "Study", "Auckland", "Block", 
    "Doran", "Gamsu", "Morrison", "Papageorgiou", 
    "Tauesch", NA, "Summary"),
  c("Deaths", "(steroid)", "36", "1", 
    "4", "14", "3", "1", 
    "8", NA, NA),
  c("Deaths", "(placebo)", "60", "5", 
    "11", "20", "7", "7", 
    "10", NA, NA),
  c("", "OR", "0.58", "0.16", 
    "0.25", "0.70", "0.35", "0.14", 
    "1.02", NA, "0.53"))

forestplot(tabletext, 
           cochrane_from_rmeta,new_page = TRUE,
           is.summary=c(TRUE,TRUE,rep(FALSE,8),TRUE),
           clip=c(0.1,2.5), 
           xlog=TRUE, 
           col=fpColors(box="royalblue",line="darkblue", summary="royalblue"))

I have a forestplot, and my x-axis tick mark labels are spaced a bit strangely, and I would like to change it to having each tick mark be 0.1 apart from each other. Also, does anyone know how forestplot decides how the ticks are spaced?

Answer 1

From the forestplot documentation (https://cran.r-project.org/web/packages/forestplot/vignettes/forestplot.html#ticks-and-grids), you have two options.

1. you can set manually in your forestplot() expression your ticks, e.g. xticks = c(-.1, -0.05, 0, .05)
2. you can create a sequence, e.g. xticks <- seq(from = -0.08, to = 2.50, by = 0.1) and add it to your forestplot() expression with xticks = xticks