ggplot2 axis as time with 1 hour error

Question

I have a question on formatting the x axis as time.

This is a sample of my data:

dput(x)
structure(list(Sample = c("BK01", "BK02", "BK03", "BK04", "BK05", 
"BK06", "BK07", "BK08", "BK09", "BK10", "BK11", "BK12", "BK13", 
"BK14", "BK15", "BK16", "BK17", "BK18", "BK19", "BK20", "BK21", 
"BK22", "BK23", "BK24", "BK25", "BK26", "BK27", "BK28", "BK29", 
"BK30", "BK31", "BK32", "BK33"), Breath.d13C = c(-25.62, -27.45, 
-26.87, -25.21, -26.01, -24.33, -24.45, -23.73, -25.05, -26.11, 
-27, -26.28, -24.62, -26.96, -24.55, -24.52, -21.24, -26.18, 
-24.82, -26.12, -27.28, -26.5, -24.46, -22.83, -27.28, -25.55, 
-27.12, -24.46, -23.07, -28.35, NA, -25.98, -26.64), Chms = structure(c(1470047400, 
1470048300, 1470048300, 1470049200, 1470050100, 1470050100, 1470040200, 
1470041100, 1470040200, 1470041100, 1470065400, 1470063600, 1470063600, 
1470064500, 1470061800, 1470045600, 1470045600, 1470046500, 1470047400, 
1470066300, 1470060000, 1470058200, 1470057300, 1470047400, 1470042000, 
1470042000, 1470041100, 1470041100, 1470040200, 1470043800, NA, 
1470060000, 1470039300), class = c("POSIXct", "POSIXt"), tzone = "")), class = "data.frame", row.names = c(NA, 
-33L), .Names = c("Sample", "Breath.d13C", "Chms"))

I want to use ggplot2 to build a graph of Breath.d13C vs Chms (Collection Time).

library(ggplot2)

ggplot(x, aes(x=Chms,y=Breath.d13C)) +
geom_point() +
  scale_y_continuous(name=expression(delta^13*C["Breath"]*" "("\u2030")),
                     limits=c(-30,-10),
                     breaks=seq(-30,-10,5),
                     labels=fmt_decimals(1)) +
  scale_x_datetime(name="Collection Time", 
                   labels = date_format("%H:00",tz="UTC"),
                   date_breaks = "1 hour") +
  my_theme

This code gives me . However the times are off by an hour. I can see this by checking the Chms column or by using the normal R plots

with this code:

plot(x$Chms,x$Breath.d13C,cex=0.8)

The two plots use the same data set, so I have no idea what's causing the error on ggplot2. I'd like to keep using it, though. Any ideas on what am I doing wrong?

Thank you in advance

`Error in check_breaks_labels(breaks, labels) : could not find function "fmt_decimals"`. Did you use this function: `fmt_dcimals <- function(decimals=0){ # return a function responpsible for formatting the # axis labels with a given number of decimals function(x) as.character(round(x,decimals)) }` And also, what si `my_theme` ? — Miha, Aug 01 '16 at 17:27

score 1 · Accepted Answer · answered Aug 01 '16 at 17:46

You need to specify the time zone in scale_x_datetime.

The function date_format() is by default set to "UTC". Therefore, your labels are converted to UTC. To use the time zone e.g. I used "Europe/London" (to get your desired output), you can do the following in your ggplot code: labels = date_format("%H:%M", tz = "Europe/London")

But firstly in order to run your code I also had to define what you specified in your code as fmt_decimals So I used this function given by @joran:

fmt_dcimals <- function(decimals=0){
   # return a function responpsible for formatting the 
   # axis labels with a given number of decimals 
   function(x) as.character(round(x,decimals))
}

So your code looks like this:

ggplot(x, aes(x=Chms,y=Breath.d13C)) +
  geom_point() +
  scale_y_continuous(name=expression(delta^13*C["Breath"]*" "("\u2030")),
                     limits=c(-30,-10),
                     breaks=seq(-30,-10,5),
                     labels=fmt_dcimals(1)) +
    scale_x_datetime(name="Collection Time", 
                   labels = date_format("%H:%M", tz = "Europe/London"),
                   date_breaks = "1 hour")

And output:

Thank you! I suspected it had to do with the time zone. But wasn't managing to work around it. (sorry I forgot to include the function for `fct_decimals` but you guessed right) — answer42, Aug 02 '16 at 09:39

score 1 · Answer 2 · answered Aug 01 '16 at 18:11

The problem lie in the time zone you select, i.e. UTC. You should choose the current time zone. The corrected code is as below

     library(ggplot2)
    ggplot(x, aes(x=Chms,y=Breath.d13C)) +
      geom_point() +
      scale_y_continuous(name=expression(delta^13*C["Breath"]*" "   
         ("\u2030")),
                 limits=c(-30,-10),
                 breaks=seq(-30,-10,5)) +
      scale_x_datetime(name="Collection Time", 
               labels = date_format("2016-08-01 %H:00",""),
               date_breaks = "1 hour")

See the plot as belpw

ggplot2 axis as time with 1 hour error

2 Answers2