Peter Peter - 1 month ago 21
R Question

legend in a forest plot

I am having a hard time with the forest plot package in R. Here is my code. Actually everything works well beside the legend.
Here is the forest plot I am generating with my code. However for the legend, I would like to have a Blue Circle, A red Square and a green losange in stead of 3 squares.

Any idea?
Thanks in advance.
Peter

library(forestplot)
test_data <- data.frame(coef1=c(0.54,0.72,0.57),
coef2=c(0.59,0.79,0.58),
coef3=c(0.49,0.60,0.48),
low1=c(0.41,0.46,0.42),
low2=c(0.44,0.49,0.42),
low3=c(0.37,0.37,0.35),
high1=c(0.72,1.12,0.77),
high2=c(0.78,1.26,0.80),
high3=c(0.65,0.99,0.66))

col_no <- grep("coef", colnames(test_data))
row_names <- list(
list("Behavioral CVH","Biological CVH","Total CVH"))

coef <- with(test_data, cbind(coef1, coef2, coef3))
low <- with(test_data, cbind(low1, low2, low3))
high <- with(test_data, cbind(high1, high2, high3))
forestplot(row_names, coef, low, high,
title="Paris Prospective Study 3",
fn.ci_norm=matrix(c("fpDrawCircleCI", "fpDrawNormalCI","fpDrawDiamondCI"),
nrow = 3, ncol=3, byrow=T),
zero = c(1), boxsize=0.05,
col=fpColors(box=c("royalblue", "gold", "black"),
line=c("darkblue", "orange", "black"),
summary=c("darkblue", "red", "black"),
hrz_lines = "#444444"),
xlab="Odds ratio & 95% Confidence intervals",
vertices = TRUE,
new_page = TRUE,
legend=c("Q2 vs. Q1","Q3 vs. Q1","Q4 vs. Q1"),
legend_args = fpLegend(pos = list("topright"),
title="Legend",
r = unit(0, "snpc"),
gp = gpar(col="#CCCCCC", lwd=1.5)))

Answer

One thing you can do is use the "regular" call to legend, outside the call for the forestplot.
To do that, you'll first have to call plot.new:

plot.new()
forestplot(...) # without the legend part
legend("topright", c("Q2 vs. Q1","Q3 vs. Q1","Q4 vs. Q1"), title="Legend", border="#CCCCCC", box.lwd=1.5, 
       col=c("blue", "red", "green"), pch=c(16, 15, 18))