Label group of plots - r

Question

I merged nine plots together and I would like to group them based on different characteristics (A,B,C). Is there a simple way to add labels or annotations at the bottom of plots? When using cowplot or GridExtra i receive the following error:
In as_grob.default(plot) :
Cannot convert object of class list into a grob.
Sample data
list(list(stats = structure(c(43, 96.5, 297.5, 707.5, 778), .Dim = c(5L,
1L)), n = 36, conf = structure(c(136.603333333333, 458.396666666667
), .Dim = 2:1), out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(2, 10.5, 55.5, 102, 128), .Dim = c(5L,
1L)), n = 36, conf = structure(c(31.405, 79.595), .Dim = 2:1),
out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(1, 3, 5.5, 77, 88), .Dim = c(5L,
1L)), n = 36, conf = structure(c(-13.9866666666667, 24.9866666666667
), .Dim = 2:1), out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(531, 632.5, 701, 726.5, 786), .Dim = c(5L,
1L)), n = 36, conf = structure(c(676.246666666667, 725.753333333333
), .Dim = 2:1), out = c(485, 464, 446), group = c(1, 1, 1
), names = ""), list(stats = structure(c(104,
109.5, 113.5, 121, 125), .Dim = c(5L, 1L)), n = 36, conf = structure(c(110.471666666667,
116.528333333333), .Dim = 2:1), out = c(91, 91, 88, 84, 84,
79), group = c(1, 1, 1, 1, 1, 1), names = ""),
list(stats = structure(c(28, 53.5, 83.5, 88, 91), .Dim = c(5L,
1L)), n = 36, conf = structure(c(74.415, 92.585), .Dim = 2:1),
out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(80, 89, 102.5, 153, 236), .Dim = c(5L,
1L)), n = 36, conf = structure(c(85.6466666666667, 119.353333333333
), .Dim = 2:1), out = c(343, 318, 299, 257), group = c(1,
1, 1, 1), names = """"), list(stats = structure(c(7,
12, 22.5, 44, 72), .Dim = c(5L, 1L)), n = 36, conf = structure(c(14.0733333333333,
30.9266666666667), .Dim = 2:1), out = numeric(0), group = numeric(0),
names = ""), list(stats = structure(c(5,
5, 6, 12.5, 21), .Dim = c(5L, 1L)), n = 36, conf = structure(c(4.025,
7.975), .Dim = 2:1), out = numeric(0), group = numeric(0),
names = ""))
Many thanks

Answer 1

I agree with the idea of using ggplot2 graphics with facets, but given your plot objects, you could do something like this (to get you started). I used ggplotify instead of cowplot because I ran into trouble with the figure margins, but you might be able to fix that by changing the null device (not tested).
Edit:
Added individual labels and y axis labels, as well as outer margins. You might have to adjust some of that depending on the output size of your composite plot. This may show you how you could adjust those settings for individual plots. Still, using ggplot2 to generate the plots would make things quite a bit easier.
library(grid)
library(gridExtra)
library(ggplotify)
sdt <- list(list(stats = structure(c(43, 96.5, 297.5, 707.5, 778), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(136.603333333333, 458.396666666667), .Dim = 2:1),
out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(2, 10.5, 55.5, 102, 128), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(31.405, 79.595), .Dim = 2:1),
out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(1, 3, 5.5, 77, 88), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(-13.9866666666667, 24.9866666666667), .Dim = 2:1),
out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(531, 632.5, 701, 726.5, 786), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(676.246666666667, 725.753333333333), .Dim = 2:1),
out = c(485, 464, 446), group = c(1, 1, 1), names = ""),
list(stats = structure(c(104, 109.5, 113.5, 121, 125), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(110.471666666667, 116.528333333333), .Dim = 2:1),
out = c(91, 91, 88, 84, 84, 79), group = c(1, 1, 1, 1, 1, 1), names = ""),
list(stats = structure(c(28, 53.5, 83.5, 88, 91), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(74.415, 92.585), .Dim = 2:1),
out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(80, 89, 102.5, 153, 236), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(85.6466666666667, 119.353333333333), .Dim = 2:1),
out = c(343, 318, 299, 257), group = c(1,1, 1, 1), names = ""),
list(stats = structure(c(7, 12, 22.5, 44, 72), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(14.0733333333333, 30.9266666666667), .Dim = 2:1),
out = numeric(0), group = numeric(0), names = ""),
list(stats = structure(c(5, 5, 6, 12.5, 21), .Dim = c(5L, 1L)),
n = 36, conf = structure(c(4.025, 7.975), .Dim = 2:1),
out = numeric(0), group = numeric(0), names = ""))
sublabels <- paste0(rep(LETTERS[1:3], each=3), 1:3)
gplts <- lapply(1:9, function(x) as.grob(function(y=sdt[[x]]) {
par(oma=c(0,3,0,3))
bxp(y, ylab="values", main=sublabels[x])}))
grid.arrange(rectGrob(gp=gpar(col="red")), rectGrob(gp=gpar(col="green")),
rectGrob(gp=gpar(col="yellow")), nrow=1, newpage =T)
vp <- viewport(.33/2,0.45, gp = gpar(col="red"))
grid.text("Group A",
y = .1, just = c("center", "bottom"),
gp = gpar(fontsize=20), vp = vp)
vp <- viewport(.5,.45, gp = gpar(col="green"))
grid.text("Group B",
y = .1, just = c("center", "bottom"),
gp = gpar(fontsize=20), vp = vp)
vp <- viewport(1-(.33/2),.45, gp = gpar(col="yellow"))
grid.text("Group C",
y = .1, just = c("center", "bottom"),
gp = gpar(fontsize=20), vp = vp)
grid.arrange(grobs=gplts, nrow=1, newpage=F)
Created on 2021-03-25 by the reprex package (v1.0.0)