Вы можете использовать следующий код, измененный с @ user213544 на цвет b и c
library(tidyverse)
a1<-data.frame(a=c(1,2,3),b=c(45,34,67),c=c(35,56,89))
a2<-data.frame(a=c(1,2,3),b=c(35,40,60),c=c(30,59,92))
a3<-data.frame(a=c(1,2,3),b=c(45,38,57),c=c(35,52,91))
df <- bind_rows(a1,a2,a3, .id = "id")
df %>% pivot_longer(-c(a,id)) %>%
ggplot(aes(x = a, y = value, colour = name)) + geom_line()+
facet_wrap(~id, labeller = labeller(id = c(`1` = "a1", `2` = "a2", `3` = "a2")))+
labs(title="Plot title",x="a", y = "b & c")
![enter image description here](https://i.stack.imgur.com/MkRKG.png)
Обновление
a1<-data.frame(a=c(1,2,3),b=c(45,34,67),c=c(35,56,89),d=c("first"))
a2<-data.frame(a=c(1,2,3),b=c(35,40,60),c=c(30,59,92),d=c("second"))
a3<-data.frame(a=c(1,2,3),b=c(45,38,57),c=c(35,52,91),d=c("third"))
df <- bind_rows(a1,a2,a3)
df %>% pivot_longer(-c(a, d)) %>%
ggplot(aes(x = a, y = value, colour = name)) + geom_line()+
facet_wrap(~d)+
labs(title="Plot title",x="a", y = "b & c")
![enter image description here](https://i.stack.imgur.com/lIG9h.png)