ggplot Time Series Figure Error: Invalid input: time_trans works with objects of class POSIXct only-CodePudding

My dataset is a dataframe with max daily temp of water over the past 4 summers.

     X site      DateTime            value Month Year  Day  
   <int> <fct>     <dttm>              <dbl> <int> <fct> <chr>
 1  6775 RAYNER_UP 2018-07-09 19:00:00  19.8     7 2018  07/10
 2  6776 RAYNER_UP 2018-07-10 19:00:00  21.2     7 2018  07/11
 3  6777 RAYNER_UP 2018-07-11 19:00:00  20.4     7 2018  07/12
 4  6778 RAYNER_UP 2018-07-12 19:00:00  20.1     7 2018  07/13
 5  6779 RAYNER_UP 2018-07-13 19:00:00  17.3     7 2018  07/14
 6  6780 RAYNER_UP 2018-07-14 19:00:00  19.5     7 2018  07/15
 7  6781 RAYNER_UP 2018-07-15 19:00:00  21.2     7 2018  07/16
 8  6782 RAYNER_UP 2018-07-16 19:00:00  21.0     7 2018  07/17
 9  6783 RAYNER_UP 2018-07-17 19:00:00  19.8     7 2018  07/18
10  6784 RAYNER_UP 2018-07-18 19:00:00  16.8     7 2018  07/19

My goal is to make a line graph with a different line for each year. So far, with a lot of help from the internet, I've made a line for each year BUT the scale is terribly packed together example.

I would like to rescale the x axis in my time series to show days of the month.

So far using scale_x_datetime, and scale_x_date in ggplot but have been unsuccessful. I keep getting the error: Invalid input: time_trans works with objects of class POSIXct only, even though the date column is in POSIXct.

Example of my code which is giving the probelm:

test1 = ggplot()  
geom_line(data = Rayner_up_summer, aes(x=strftime(DateTime,format="%m/%d"),
                                  y=value, 
                                group = Year,
                                  color=strftime(DateTime,format="%Y"))) 
                               # size=.1)) 
 scale_color_discrete(name="Year") 
 labs(x="date")

Does anyone know why I am unable to use scale_x_datetime even though my x axis (DateTime) is in POSIXct Date Time format? I would appreciate any advice you might have

CodePudding user response：

As I said in my comment, the issue is that you convert your DateTime column to a character via strftime(DateTime,format="%m/%d") which is the reason why your scale get terribly packed together and also the reason why scale_x_date or _datetime will not work.

Instead, one option to achieve your desired result would be

Add a helper date column to your data where you use the same year.
Map this helper date column on x

Note: I slightly altered your dataset to account for a second year.

Rayner_up_summer$DateTime <- as.Date(paste0("2018/", Rayner_up_summer$Day))

library(ggplot2)

ggplot()  
  geom_line(data = Rayner_up_summer, aes(
    x = DateTime,
    y = value,
    group = Year,
    color = factor(Year)
  ))  
  scale_x_date(date_labels = "%m/%d")  
  scale_color_discrete(name = "Year")  
  labs(x = "date")

DATA

Rayner_up_summer <- structure(list(X = c(
  6775L, 6776L, 6777L, 6778L, 6779L, 6780L,
  6781L, 6782L, 6783L, 6784L, 6775L, 6776L, 6777L, 6778L, 6779L,
  6780L, 6781L, 6782L, 6783L, 6784L
), site = c(
  "RAYNER_UP", "RAYNER_UP",
  "RAYNER_UP", "RAYNER_UP", "RAYNER_UP", "RAYNER_UP", "RAYNER_UP",
  "RAYNER_UP", "RAYNER_UP", "RAYNER_UP", "RAYNER_UP", "RAYNER_UP",
  "RAYNER_UP", "RAYNER_UP", "RAYNER_UP", "RAYNER_UP", "RAYNER_UP",
  "RAYNER_UP", "RAYNER_UP", "RAYNER_UP"
), DateTime = structure(c(
  1531173600,
  1531260000, 1531346400, 1531432800, 1531519200, 1531605600, 1531692000,
  1531778400, 1531864800, 1531951200, 1531173600, 1531260000, 1531346400,
  1531432800, 1531519200, 1531605600, 1531692000, 1531778400, 1531864800,
  1531951200
), class = c("POSIXct", "POSIXt"), tzone = ""), value = c(
  19.8,
  21.2, 20.4, 20.1, 17.3, 19.5, 21.2, 21, 19.8, 16.8, 21.5740302174818,
  21.6853770664893, 18.4306976739317, 21.1522381303366, 20.208727594465,
  19.5954797456507, 20.6829415732063, 17.6733329861891, 20.2849614520092,
  20.5253239201847
), Month = c(
  7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L,
  7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L
), Year = c(
  2018,
  2018, 2018, 2018, 2018, 2018, 2018, 2018, 2018, 2018, 2019, 2019,
  2019, 2019, 2019, 2019, 2019, 2019, 2019, 2019
), Day = c(
  "07/10",
  "07/11", "07/12", "07/13", "07/14", "07/15", "07/16", "07/17",
  "07/18", "07/19", "07/10", "07/11", "07/12", "07/13", "07/14",
  "07/15", "07/16", "07/17", "07/18", "07/19"
)), row.names = c(
  "1",
  "2", "3", "4", "5", "6", "7", "8", "9", "10", "11", "21", "31",
  "41", "51", "61", "71", "81", "91", "101"
), class = "data.frame")