ggplot2 axis as time with 1 hour error [duplicate] - r

Question

This question already has answers here:
Time series plot gets offset by 2 hours if scale_x_datetime is used
(2 answers)
Closed 6 years ago.
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

Answer 1

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:

Answer 2

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