The package provides several functions to modify the forest plot.
Below are the functions to edit various aspects of the plot:
Editing the Plot
Below, we make the total row text bold, change the color of the
diamond shape, and modify the background color of the total row. We also
align text in the last six columns to the center.
# Change font face
g <- edit_plot(p, row = 9,
gp = gpar(fontface = "bold"))
# Change color
g <- edit_plot(g, col = 8, row = 9, which = "ci",
gp = gpar(col = "blue", fill = "blue"))
# Change the background of the total row
g <- edit_plot(g, col = 1:7,
row = 9,
which = "background",
gp = gpar(fill = "#f6eff7"))
# Align text to center
g <- edit_plot(g, col = 9:14,
which = "text",
hjust = unit(0.5, "npc"),
x = unit(0.5, "npc"))
g
For text alignment: - hjust = unit(0, "npc") and
x = unit(0, "npc") align text to the left. -
hjust = unit(0.5, "npc") and
x = unit(0.5, "npc") center-align text. -
hjust = unit(1, "npc") and
x = unit(0.9, "npc") align text to the right.
Adding and Inserting Text
In this step, we add some text to the header and total number of
events in the data.
# Add or insert some text to the header on top of CI columns
g <- add_text(g, text = "IV, Random, 95% CI",
part = "header",
col = 7:8,
gp = gpar(fontface = "bold"))
g <- insert_text(g, text = "Odds ratio",
part = "header",
col = 7:8,
gp = gpar(fontface = "bold"))
# Group outcomes
g <- add_text(g, text = "Caffeine",
part = "header",
row = 1,
col = 2:3,
gp = gpar(fontface = "bold"))
g <- add_text(g, text = "Decaf",
part = "header",
row = 1,
col = 4:5,
gp = gpar(fontface = "bold"))
# Add text on the top of the risk of bias data
g <- add_text(g, text = "Risk of Bias",
part = "header",
row = 1,
col = 9:14,
gp = gpar(fontface = "bold"))
# Insert event count
g <- insert_text(g,
text = c("Total events:"),
row = 9,
col = 1,
before = FALSE,
just = "left")
# Note: The row counts need to add one to account for
# `insert_text` in the previous step
g <- add_text(g, text = "58",
col = 2,
row = 10,
just = "left")
g <- add_text(g, text = "46",
col = 4,
row = 10,
just = "left")
g
Adding Borders
In the next step, we add some borders to the header. The default is
to add a border at the bottom of the cell(s).
# Add or insert some text to the header
g <- add_border(g,
part = "header",
row = 1,
col = 9:14,
gp = gpar(lwd = .5))
g <- add_border(g,
part = "header",
row = 2,
gp = gpar(lwd = 1))
g
Adding Grobs
In the next step, we add a rounded rectangle border with a dashed
line around the risk of bias data. Then, we draw a circle grob with
different colors at the bottom of the text.
g <- add_grob(g,
row = 1:c(nrow(dt_fig) - 1),
col = 9:14,
order = "background",
gb_fn = roundrectGrob,
r = unit(0.05, "snpc"),
gp = gpar(lty = "dotted",
col = "#bdbdbd"))
# Draw a circle grob; you can also draw a `pointsGrob`
cols <- c("#eeee00", "#00cc00", "#cc0000")
symb <- c("?", "+", "-")
for(i in seq_along(symb)){
pos <- which(dt_fig == symb[i], arr.ind = TRUE)
for(j in 1:nrow(pos)){
g <- add_grob(g,
row = pos[j, 1],
col = pos[j, 2],
order = "background",
gb_fn = circleGrob,
r = 0.4,
gp = gpar(fill = cols[i]))
}
}
g
The text we are going to create involves math expressions and
multiple lines. Any one of these can easily be done with
add_text and setting parse = TRUE. We can use
the code below to achieve what we want. The line break below is based on
the solution here
using the atop function. You can also use the latex2exp
package for math expressions.
txt <- bquote(atop(paste("Heterogeneity: ", tau^2, " = 0.22; ",
chi^2, " = 9.39, df = 6 (P = 0.15) ",
I^2, " = 36%"),
"Total for overall effect: Z = 1.15 (P = 0.25)"))
add_text(g, text = txt,
col = 1:6,
row = 11,
just = "left",
parse = TRUE,
gp = gpar(fontsize = 8))
We can see that the second line is not left-aligned. We can use
add_grob to take advantage of other packages that create
grobs objects. Now we will use the gridtext package
to generate complex text and add it to the plot with
add_grob. More details about the package can be found here. You can write
markdown or HTML text and render it to the plot. Currently, it does not
support math equations. See other Unicode math symbols here.
txt <- "Heterogeneity: τ<sup>2</sup> = 0.22; χ<sup>2</sup> = 9.39,
df = 6 (P = 0.15); I<sup>2</sup> = 36%<br><span style='color:blue'>**Total for overall effect:**</span> Z = 1.15 (P = 0.25)"
add_grob(g,
row = 11,
col = 1:6,
order = "background",
gb_fn = gridtext::richtext_grob,
text = txt,
gp = gpar(fontsize = 8),
hjust = 0, vjust = 1, halign = 0, valign = 1,
x = unit(0, "npc"), y = unit(1, "npc"))
