更改 ggplot 中 x 轴标签的顺序

Question

I have dates as 'Dec-17','Jan-18','Feb-18','Mar-18','Apr-18','May-18','Jun-18','Jul-18','Aug-18' When I plot I need to preserve this in x axis. But x axis is getting reordered. I tried factors method, then also I get the same :

> data_$Dates
[1] Apr-18 Aug-18 Dec-17 Feb-18 Jan-18 Jul-18 Jun-18 Mar-18 May-18
9 Levels: Apr-18 Aug-18 Dec-17 Feb-18 Jan-18 Jul-18 Jun-18 ... May-18

But, I need to follow the same formatting starting from Dec-17 and not Apr-18 My code :

data_$Dates <- factor(data_$Dates, levels = data_$Dates[order(data_$`Expected`)])
data_$Dates
ggplot(data=data_, aes(x=Dates, y=`Expected`, group=1)) +
  geom_line()+
  geom_point()

Answer 1

You're reordering alphabetically. You'll probably want to either convert your data to a data type that is interpreted as such (as suggested by @Wimpel in his/her comment). Alternatively, as you only have 9 unique values, you may want to reorder manually:

date_$Dates <- factor(date_$Dates, levels = c("Dec-17", "Jan-18", "Feb-18"))

(which you'll have to expand to include the six months I have omitted).

Answer 2

Let's generate some sample data first:

set.seed(123)
data_ <- data.frame(Expected = sample(1:10, 9), Dates = c('Dec-17','Jan-18',
    'Feb-18','Mar-18', 'Apr-18', 'May-18','Jun-18', 'Jul-18', 'Aug-18'),
    stringsAsFactors = FALSE)

As @Wimpel told, the most natural way is to transform your data-column into a Data-type column. Here you may find a comprehensive discussion on possible ways for that. One of the most convenient solutions is using of the lubridate package:

library(lubridate)
data_$Dates_data <-  as.Date(parse_date_time(data_$Dates, "m-y"))

Now you have a date-formatted column to be used as x-data, and you may adjust the format of x labels according to your preferences (again, as @Wimpel suggested):

pl_1 <- ggplot(data = data_, aes(x = Dates_data, y = Expected, 
    group = 1)) +
  geom_line() +
  geom_point() +
  scale_x_date(date_labels = "%b-%y", date_breaks = "1 month")
plot(pl_1)