Converting POSIXct to Julian Dates in ggplot

Question

I have been trying to convert POSIXct format so that my date and times would reflect Julian dates.

ind$DateAndTime <- as.POSIXct(ind$DateAndTime, tz = "UTC",
                                  origin = '1970-01-01')

ind$DateAndTime<- format(as.POSIXct(ind_steps$t2),"%y%j")

I had used these two lines of code to do so, but I am now having trouble plotting them using ggplot.

    plot_list[[i]]  <- ggplot(ind, aes(x = DateAndTime, y = NSD)) + 
      geom_line() + theme_bw() +
      ggtitle(random_tables[i]) +
      theme(axis.text.x = element_text(angle = 90))

When I plot it I get this, where the julian dates are vertical, but they still overlap. I would like to get the graph to show the julian dates more visibly and to show every other julian date so that it isn't so cramped in the x-axis. Is there a way to do this?

It's easier to help you if you include a simple [reproducible example](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) with sample input and desired output that can be used to test and verify possible solutions. Rather than changing your data to character values, it probably make more sense to just format the date/time access. — MrFlick, Apr 18 '21 at 00:48

Dave2e · Accepted Answer · 2021-04-18T01:12:30.647

Here is the completed code. Without any sample data, it is difficult to provide an exact example.

From your previous question, your issue maybe related to attempting to pass a datetime object to a function expecting a date object. In this case I used as.Date() and scale_x_date(), in your case you may want to use as.POSIXct() and scale_x_datetime()

#create dummy data
DateAndTime = 18000:18300
NSD = DateAndTime/10000
ind <-data.frame(DateAndTime, NSD)

#convert the DateAndTime column into a date object
ind$DateAndTime <- as.Date(ind$DateAndTime, tz = "UTC",
                              origin = '1970-01-01')

#Plot table and format x-axis
ggplot(ind, aes(x = DateAndTime, y = NSD)) + 
   geom_line() + theme_bw() +
   ggtitle("Demo Title") +
   scale_x_date(date_breaks = "1 month", date_labels = "%y-%j")
   theme(axis.text.x = element_text(angle = 90))

Converting POSIXct to Julian Dates in ggplot

1 Answers1