R：How can use ggplot2 order month x axis

Question

My data like this,but draw plot x axis is 12_01 12_10 12_11 12_12 12_2 I want to like 12_01 12_02 12_03...... 12_12 How can do it? thanks!

df=data.frame(year=12,
              month=1:12,
              g=c(10,20,14,15,11:18))

df2 <- df %>%
    arrange(month) %>%
    unite(year_month,year,month) %>%
    group_by(year_month) 


ggplot(df2 , aes(x = year_month, y =g,group = 1))+  
  geom_line() + 
  geom_point(shape = 22, size = 2, fill = "white")

Answer 1

You could manage this by converting year_month into a factor; or alternatively using {lubridate}...

library(dplyr)
library(tidyr)
library(ggplot2)
library(stringr)

df=data.frame(year=12,
              month=1:12,
              g=c(10,20,14,15,11:18))

df2 <- df %>%
  arrange(month) %>%
  unite(year_month,year,month) %>%
  mutate(year_month = factor(year_month, levels = paste0("12_", 1:12))) %>% 
  group_by(year_month) 


ggplot(df2 , aes(x = year_month, y =g,group = 1))+  
  geom_line() + 
  geom_point(shape = 22, size = 2, fill = "white")

Alternatively with lubridate if you want to preserve the variable as a date object:

df2 <- df %>%
  arrange(month) %>%
  unite(year_month,year,month) %>%
  mutate(year_month = ym(year_month)) %>% 
  group_by(year_month) 

ggplot(df2 , aes(x = year_month, y =g,group = 1))+  
  geom_line() + 
  geom_point(shape = 22, size = 2, fill = "white")+
  scale_x_date(date_labels = "%y_%m",
               date_breaks = "1 month") 

^{Created on 2022-03-18 by the reprex package (v2.0.1)}

Answer 2

Why not make them into actual dates?

df %>%
  arrange(month) %>%
  mutate(date = as.Date(paste(paste0(20, year), month, 1, sep = '-'))) %>%
  ggplot(aes(x = date, y =g,group = 1))+  
  geom_line() + 
  geom_point(shape = 22, size = 2, fill = "white")

Answer 3

My recommdation is to create a date variable in you dataframe and use that in the x axis, that way is more flexible de axis label configuration, via scale_x_date().

Look at two options:

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

df <- data.frame(year = 12, month = 1:12, g = c(10, 20, 14, 15 , 11:18))

df2 <- df %>%
  mutate(
    date = make_date(year + 2000, month, "01")
  ) 

ggplot(df2, aes(x = date, y = g)) +  
  geom_line() + 
  geom_point(shape = 22, size = 2, fill = "white") +
  scale_x_date(labels = ~format(., '%m_%y'))

ggplot(df2, aes(x = date, y = g)) +  
  geom_line() + 
  geom_point(shape = 22, size = 2, fill = "white") +
  scale_x_date(labels = ~format(., '%b %y'))

^{Created on 2022-03-18 by the reprex package (v2.0.1)}