The package has some functionality to modify the forest plot. Below
are the functions to edit various aspects of the plot:
Edit plot
Below is to make the total row text bold and change the color of the
diamond shape. Then change the background color of the total row. After
that, align texts 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 texts to center
g <- edit_plot(g, col = 9:14,
which = "text",
# gp = gpar(),
hjust = unit(0.5, "npc"),
x = unit(0.5, "npc"))
g
For the text-align, hjust = unit(0, "npc") and
x = unit(0, "npc") to align left.
hjust = unit(0.5, "npc") and
x = unit(0.5, "npc") to align the text in the center.
hjust = unit(1, "npc") and
x = unit(0.9, "npc") to align right.
Add and insert text
In this step, we want to 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
Add borders
In the next step, we will add some borders at 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
Add grobs
In the next step, we will add a rounded rectangle border with a
dashed line around the risk of bias data. Then 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 latex2exp
package for math expression.
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 a 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"))
