In ggplot2, how can I use multi-row x-axis labels with facet

I have multi-row x-axis labels such that the first row is month and the second row is year. However, I run into check_aesthetics() errors when I try to use the multi-row axis labels with facet_wrap().

Example Data:

library(data.table)
library(dplyr)
library(ggplot2)

df1 <- data.frame(matrix(ncol = 3, nrow = 12))
colnames(df1)[1:3] <- c("Date", "Group", "Value")
df1$Date <- rep(seq.Date(as.Date("2020-03-14"),as.Date("2020-08-20"),"1 month"),2)
df1$Group <- sort(rep(c("A","B"),6))
df1$Value <- rnorm(12,50,10)
df1 <- df1 %>%
  mutate(Month = month(Date),
         Year = year(Date),
         date = zoo::as.yearmon(paste(Year, Month), "%Y %m"))

df2 <- data.frame(matrix(ncol = 3, nrow = 12))
colnames(df2)[1:3] <- c("Date", "Group", "Value")
df2$Date <- rep(seq.Date(as.Date("2021-03-14"),as.Date("2021-08-20"),"1 month"),2)
df2$Group <- sort(rep(c("A","B"),6))
df2$Value <- rnorm(12,50,10)
df2 <- df2 %>%
  mutate(Month = month(Date),
         Year = year(Date),
         date = zoo::as.yearmon(paste(Year, Month), "%Y %m"))

df3 <- rbind(df1,df2)

cols <- c("A" = "#ca0020", "B" = "#0571b0")

Figure without facet_wrap() showing the multi-row x-axis

ggplot(data = df3, aes(x = factor(date), y = Value, color = Group, group = paste(Year,Group)))  
  geom_line()  
  geom_point(size = 3, aes(fill = Group), color = "black", shape = 21)  
  scale_fill_manual(values = cols)  
  scale_color_manual(values = cols)  
  scale_x_discrete(labels=substr(df3$date,1,3)) 
  labs(x = "")  
  theme_bw()  
  theme(plot.margin = unit(c(1, 1, 2, 1), "lines"),
        panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"),
        legend.title = element_blank(),
        legend.direction = "horizontal",
        legend.margin = margin(),
        legend.background = element_blank(),
        legend.position = c(0.1,0.93),
        panel.border = element_blank())  
  guides(fill = guide_legend(nrow = 2))  
  coord_cartesian(clip = 'off', ylim = c(0, 100))  
  annotation_custom(grid::rectGrob(gp = grid::gpar(fill = NA)))  
  annotate(geom = "text", x = c(3.5,9.5), y = -15, label = unique(df3$Year), size = 6)  
  annotate('rect',
           xmin = 6.35,
           xmax = 6.65,
           ymin = -10, ymax = 0, fill = 'white')  
  annotate('segment',
           x = c(6.35, 6.65),
           xend = c(6.35, 6.65), y = -10, yend = 0)

Now when I try to add the facet_wrap()...

ggplot(data = df3, aes(x = factor(date), y = Value, color = Group, group = paste(Year,Group)))  
  geom_line()  
  geom_point(size = 3, aes(fill = Group), color = "black", shape = 21)  
  scale_fill_manual(values = cols)  
  scale_color_manual(values = cols)  
  scale_x_discrete(labels=substr(df3$date,1,3)) 
  labs(x = "")  
  theme_bw()  
  theme(plot.margin = unit(c(1, 1, 2, 1), "lines"),
        panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"),
        legend.title = element_blank(),
        legend.direction = "horizontal",
        legend.margin = margin(),
        legend.background = element_blank(),
        legend.position = c(0.1,0.93),
        panel.border = element_blank())  
  guides(fill = guide_legend(nrow = 2))  
  coord_cartesian(clip = 'off', ylim = c(0, 100))  
  annotation_custom(grid::rectGrob(gp = grid::gpar(fill = NA)))  
  annotate(geom = "text", x = c(3.5,9.5), y = -15, label = unique(df3$Year), size = 6)  
  annotate('rect',
           xmin = 6.35,
           xmax = 6.65,
           ymin = -10, ymax = 0, fill = 'white')  
  annotate('segment',
           x = c(6.35, 6.65),
           xend = c(6.35, 6.65), y = -10, yend = 0)  
  facet_wrap(~Group)

...it throws the error Error in `check_aesthetics()`: ! Aesthetics must be either length 1 or the same as the data (4): label.

The error resides within annotate(geom = "text", x = c(3.5,9.5), y = -15, label = unique(df3$Year), size = 6) but I can't figure out how to fix it. I have tried changing the label = and the x = but no luck. The ideal figure would have two plots, each with multi-row x-axis labels where, similar to the example figure above, the top row is month and the second row is year. Any thoughts on how to achieve this?

CodePudding user response：

One kind of hacky way to do this is to just make two text annotations

ggplot(data = df3, aes(x = factor(date), y = Value, color = Group, group = paste(Year,Group)))  
  geom_line()  
  geom_point(size = 3, aes(fill = Group), color = "black", shape = 21)  
  scale_fill_manual(values = cols)  
  scale_color_manual(values = cols)  
  scale_x_discrete(labels=substr(df3$date,1,3)) 
  labs(x = "")  
  theme_bw()  
  theme(plot.margin = unit(c(1, 1, 2, 1), "lines"),
        panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"),
        legend.title = element_blank(),
        legend.direction = "horizontal",
        legend.margin = margin(),
        legend.background = element_blank(),
        legend.position = c(0.1,0.93),
        panel.border = element_blank())  
  guides(fill = guide_legend(nrow = 2))  
  coord_cartesian(clip = 'off', ylim = c(0, 100))  
  annotation_custom(grid::rectGrob(gp = grid::gpar(fill = NA)))  
  annotate(geom = "text", x = c(3.5), y = -15, label = 2020, size = 6)  
  annotate(geom = "text", x = c(9.5), y = -15, label = 2021, size = 6)  
  annotate('rect',
           xmin = 6.35,
           xmax = 6.65,
           ymin = -10, ymax = 0, fill = 'white')  
  annotate('segment',
           x = c(6.35, 6.65),
           xend = c(6.35, 6.65), y = -10, yend = 0)  
  facet_wrap(~Group)

CodePudding user response：

If you don't mind moving the year value to the strip you could use ggh4x package.

library(dplyr)
library(ggplot2)
library(lubridate)
library(ggh4x)

ggplot(data = df3, aes(x = factor(date), y = Value, color = Group, group = paste(Year,Group)))  
  geom_line()  
  geom_point(size = 3, aes(fill = Group), color = "black", shape = 21)  
  scale_fill_manual(values = cols)  
  scale_color_manual(values = cols)  
  scale_x_discrete(labels=substr(df3$date,1,3)) 
  labs(x = NULL)  
  theme_bw()  
  theme(plot.margin = unit(c(1, 1, 2, 1), "lines"),
        panel.grid = element_blank(),
        text = element_text(size = 16),
        axis.text.x = element_text(size = 14, color = "black", angle = 90, vjust = 0.5, hjust = 1),
        axis.text.y = element_text(size = 14, color = "black"),
        legend.title = element_blank(),
        legend.direction = "horizontal",
        legend.margin = margin(),
        legend.background = element_blank(),
        legend.position = c(0.1,0.90),
        panel.border = element_blank())  
  guides(fill = guide_legend(nrow = 2))  
  coord_cartesian(clip = 'off', ylim = c(0, 100))  
  facet_nested(~Group   Year, scales = "free_x")

^{Created on 2022-10-12 with reprex v2.0.2}