Change the multi-label X-axis label in R

Question

i have this code

library(dplyr)
library(tidyr)
library(ggplot2)
library(ggprism)

MLE <- c(0.01866, 0.015364, 0.015821, 0.008736, 0.008433,   0.008655,   0.003426,   0.003403,   0.00352)
KS <- c(0.021095,   0.016748,   0.017564,   0.010222,   0.009470,   0.009559,   0.003929,   0.003907,   0.00396)
AD <- c(0.020344,   0.016381,   0.016299,   0.009494,   0.008962,   0.009009,   0.003645,   0.003625,   0.003698)
CS <- c(0.021689,   0.017805,   0.017741,   0.010436,   0.009783,   0.00986,    0.004007,   0.004073,   0.00404)

df <- structure(list(A = c(50, 50, 50, 100, 100, 100, 250, 250, 250),
                     R = c("R1", "R2", "R3", "R1", "R2", "R3", "R1", "R2", "R3"), 
                     MLE = MLE, 
                     KS = KS, 
                     AD = AD, 
                     CS = CS, 
                     `round(2)` = c(2, 2, 2, 2, 2, 2, 2, 2, 2)),
                class = "data.frame", row.names = c(NA, -9L))

df %>% 
  pivot_longer(MLE:CS) %>% 
  mutate(across(where(is.character), as.factor)) %>% 
  ggplot(aes(x = R, y = value, group=name, col=name)) +
  geom_line(linewidth = 1.2) +
  geom_point(size=2.5) +
  xlab("") +
  ylab("Mean Square Errors") +
  scale_color_grey() + 
  theme_classic() +
  facet_wrap(~A, nrow=1, strip.position="bottom")

which draws a graph like this

I would like to do several things:

1- change the numbers in the rectangles (ie 50, 100, and 250) to m=50, m=100, and m=250, respectively

2- Make the R1, R2, and R3 bolded for all of them

Regarding the first one my attempt is this:

library(dplyr)
library(tidyr)
library(ggplot2)
library(ggprism)

MLE <- c(0.01866, 0.015364, 0.015821, 0.008736, 0.008433,   0.008655,   0.003426,   0.003403,   0.00352)
KS <- c(0.021095,   0.016748,   0.017564,   0.010222,   0.009470,   0.009559,   0.003929,   0.003907,   0.00396)
AD <- c(0.020344,   0.016381,   0.016299,   0.009494,   0.008962,   0.009009,   0.003645,   0.003625,   0.003698)
CS <- c(0.021689,   0.017805,   0.017741,   0.010436,   0.009783,   0.00986,    0.004007,   0.004073,   0.00404)

df <- structure(list(A = c(paste("m", 50, sep = "="), paste("m", 50, sep = "="), paste("m", 50, sep = "="), 
                           paste("m", 100, sep = "="), paste("m", 100, sep = "="), paste("m", 100, sep = "="), 
                           paste("m", 250, sep = "="), paste("m", 250, sep = "="), paste("m", 250, sep = "=")),
                     R = c("R1", "R2", "R3", "R1", "R2", "R3", "R1", "R2", "R3"), 
                     MLE = MLE, 
                     KS = KS, 
                     AD = AD, 
                     CS = CS, 
                     `round(2)` = c(2, 2, 2, 2, 2, 2, 2, 2, 2)),
                class = "data.frame", row.names = c(NA, -9L))

df %>% 
  pivot_longer(MLE:CS) %>% 
  mutate(across(where(is.character), as.factor)) %>% 
  ggplot(aes(x = R, y = value, group=name, col=name)) +
  geom_line(linewidth = 1.2) +
  geom_point(size=2.5) +
  xlab("") +
  ylab("Mean Square Errors") +
  scale_color_grey() + 
  theme_classic() +
  facet_wrap(~A, nrow=1, strip.position="bottom")

And the result is

The issue is that the order is messed up now even though the data points themselves are still correct, I tried rearranging the values in the data frame but to no avail.

Regarding the second issue, I don't even know where to start. So any help regarding the bolding would be appreciated

Answer 1

To get the facets in the correct order, you need to have the levels of the factor variables in the desired order. In your case, the correct order would just be unique(A) , so mutate(A = factor(A, unique(A))) should do the trick. For the bold text, use the axis.text.x element in theme :

df %>% 
  pivot_longer(MLE:CS) %>% 
  mutate(across(where(is.character), as.factor)) %>%
  mutate(A = factor(A, levels = unique(A))) %>%
  ggplot(aes(x = R, y = value, group=name, col=name)) +
  geom_line(linewidth = 1.2) +
  geom_point(size=2.5) +
  xlab("") +
  ylab("Mean Square Errors") +
  scale_color_grey() + 
  theme_classic() +
  facet_wrap(~A, nrow=1, strip.position="bottom") +
  theme(axis.text.x = element_text(size = 14, face = 'bold'))

Answer 2

A second option would be to use a custom labeller function to add the prefix to the strip text. For the axis text you could use theme option axis.text.x :

prepender <- function(x, prefix = "m=") paste0(prefix, x)

df %>%
  pivot_longer(MLE:CS) %>%
  mutate(across(where(is.character), as.factor)) %>%
  ggplot(aes(x = R, y = value, group = name, col = name)) +
  geom_line(linewidth = 1.2) +
  geom_point(size = 2.5) +
  xlab("") +
  ylab("Mean Square Errors") +
  scale_color_grey() +
  theme_classic() +
  theme(axis.text.x = element_text(face = "bold")) +
  facet_wrap(~A, nrow = 1, strip.position = "bottom", labeller = as_labeller(prepender))