R ggplot2 plotting hourly data

Question

I am trying to plot hourly meteorological data coming from a meteorological station with ggplot2 (it's my first time with ggplot). I've managed to plot daily data but having some problem when downscaling to hourly data. Data files look like that:

FECHA H_SOLAR;DIR_M;VEL_M;TEMP_M;HR;PRECIP
01/06/14 00:50:00;314.3;1.9;14.1;68.0;-99.9
01/06/14 01:50:00;322.0;1.6;13.3;68.9;-99.9
01/06/14 02:50:00;303.5;2.1;12.3;70.9;-99.9
01/06/14 03:50:00;302.4;1.6;11.6;73.1;-99.9
01/06/14 04:50:00;306.5;1.2;10.9;76.4;-99.9
01/06/14 05:50:00;317.1;0.8;12.6;71.5;-99.9
01/06/14 06:50:00;341.8;0.0;17.1;58.8;-99.9
01/06/14 07:50:00;264.6;1.2;21.8;44.9;-99.9
01/06/14 08:50:00;253.8;2.9;24.7;32.2;-99.9
01/06/14 09:50:00;254.6;3.7;26.7;27.7;-99.9
01/06/14 10:50:00;250.7;4.3;28.3;24.9;-99.9
01/06/14 11:50:00;248.5;5.3;29.1;22.6;-99.9
01/06/14 12:50:00;242.8;4.7;30.3;20.4;-99.9
01/06/14 13:50:00;260.7;4.9;31.3;17.4;-99.9
01/06/14 14:50:00;251.8;5.1;31.9;17.1;-99.9
01/06/14 15:50:00;258.1;4.6;32.4;15.3;-99.9
01/06/14 16:50:00;254.3;5.7;32.4;14.0;-99.9
01/06/14 17:50:00;252.5;4.6;32.0;14.1;-99.9
01/06/14 18:50:00;257.4;3.8;31.1;14.9;-99.9
01/06/14 19:50:00;135.8;4.2;26.0;41.2;-99.9
01/06/14 20:50:00;126.0;1.7;23.5;48.7;-99.9
01/06/14 21:50:00;302.8;0.7;21.6;53.9;-99.9
01/06/14 22:50:00;294.2;1.1;19.3;67.4;-99.9
01/06/14 23:50:00;308.5;1.0;17.5;72.4;-99.9

I have used this R commands to plot the data:

datos=read.csv("utiel.dat",sep=";",header=T,na.strings="-99.9")

dia=as.Date(datos[,1],"%y/%m/%d")       # Crear índice dia
veloc=zoo(datos[,c("VEL_M")],dia)       

gveloc=ggplot(data=datos,aes(dia,veloc))

gveloc + geom_point(colour="blue",cex=1) + ylab("Velocidad (km/h)") + xlab("Fecha") + opts(title="Velocidad media horaria") + scale_x_date(limits = as.Date(c("2007-01-01","2007-01-31")),format = "%Y-%m-%d")

and got this monthly graph with all data from a single day in the same x coordinate (i.e. the same day as it could be expected)

Hourly wind data with ggplot2

How can I manage to read not only the day but the time so each point can be plotted in it's own x/time coordinate? I think the problem starts before plotting but I couldn't find how to read date as YY/MM/DD H:M:S

Thanks in advance

Solution: Just an addition to put the code has worked for me

 datos$dia=as.POSIXct(datos[,1], format="%y/%m/%d %H:%M:%S")  # Read date/time as POSIXct

 ggplot(data=datos,aes(x=dia, y=TEMP_M)) + 
   geom_point(colour="red") + 
   ylab("Temperatura (ºC)") + 
   xlab("Fecha") + 
   opts(title="Temperatura media") + 
   scale_x_datetime(limits=c(as.POSIXct('2008/02/01'), as.POSIXct('2008/02/02')) ,format =  "%Y-%m-%d")

Hope it helps someone else, thanks Andrie and G.Grothendieck

Hi, I can't see your full coment – pacomet Nov 09 '11 at 22:06 — pacomet, Nov 09 '11 at 22:06

score 13 · Accepted Answer · answered Oct 03 '11 at 15:10

as.Date only capture the date element. To capture time, you need to use as.POSIXct:

Recreate your data:

zz <- tempfile()
cat("
FECHA H_SOLAR;DIR_M;VEL_M;TEMP_M;HR;PRECIP
01/06/14 00:50:00;314.3;1.9;14.1;68.0;-99.9
01/06/14 01:50:00;322.0;1.6;13.3;68.9;-99.9
01/06/14 02:50:00;303.5;2.1;12.3;70.9;-99.9
01/06/14 03:50:00;302.4;1.6;11.6;73.1;-99.9
01/06/14 04:50:00;306.5;1.2;10.9;76.4;-99.9
01/06/14 05:50:00;317.1;0.8;12.6;71.5;-99.9
01/06/14 06:50:00;341.8;0.0;17.1;58.8;-99.9
01/06/14 07:50:00;264.6;1.2;21.8;44.9;-99.9
01/06/14 08:50:00;253.8;2.9;24.7;32.2;-99.9
01/06/14 09:50:00;254.6;3.7;26.7;27.7;-99.9
01/06/14 10:50:00;250.7;4.3;28.3;24.9;-99.9
01/06/14 11:50:00;248.5;5.3;29.1;22.6;-99.9
01/06/14 12:50:00;242.8;4.7;30.3;20.4;-99.9
01/06/14 13:50:00;260.7;4.9;31.3;17.4;-99.9
01/06/14 14:50:00;251.8;5.1;31.9;17.1;-99.9
01/06/14 15:50:00;258.1;4.6;32.4;15.3;-99.9
01/06/14 16:50:00;254.3;5.7;32.4;14.0;-99.9
01/06/14 17:50:00;252.5;4.6;32.0;14.1;-99.9
01/06/14 18:50:00;257.4;3.8;31.1;14.9;-99.9
01/06/14 19:50:00;135.8;4.2;26.0;41.2;-99.9
01/06/14 20:50:00;126.0;1.7;23.5;48.7;-99.9
01/06/14 21:50:00;302.8;0.7;21.6;53.9;-99.9
01/06/14 22:50:00;294.2;1.1;19.3;67.4;-99.9
01/06/14 23:50:00;308.5;1.0;17.5;72.4;-99.9
", file=zz)

datos=read.csv(zz, sep=";", header=TRUE, na.strings="-99.9")

Convert dates to POSIXct and print:

library(ggplot2)

datos=read.csv(zz, sep=";", header=TRUE, na.strings="-99.9")

datos$dia=as.POSIXct(datos[,1], format="%y/%m/%d %H:%M:%S")  

ggplot(data=datos,aes(x=dia, y=TEMP_M)) + 
  geom_path(colour="red") + 
  ylab("Temperatura (ºC)") + 
  xlab("Fecha") + 
  opts(title="Temperatura media")

enter image description here

Nice answer Andrie, thanks. It works fine with the daily data I posted but the point is that my data spans for ten years. Then I need to set the set_x_scale option to choose the time period I want to plot (day to months). I am not able to reproduce the graph for a month. Is it necessary to recreate the data? — pacomet, Oct 03 '11 at 15:37
You'll have to specify your limits to the scale also as `POSIXct` dates, not `as Date`. — Andrie, Oct 03 '11 at 16:29
How should I set the limits as POSIXct? Maybe something like: `scale_x_date(limits = as.POSIXct(c("2004-01-01", "2005-01-01")), format = "%Y-%m-%d")` ?? Thanks — pacomet, Oct 04 '11 at 08:17
Hi, I've finally found how to set the x axis limits as POSIX.ct. Thank you very much for your help — pacomet, Oct 04 '11 at 09:54

G. Grothendieck · Answer 2 · 2011-10-07T15:18:27.647

Since you are using zoo we can use read.zoo to set up the data, z, and then plot it using plot.zoo, xyplot.zoo or ggplot2's qplot. We show all three below.

Lines <- "FECHA H_SOLAR;DIR_M;VEL_M;TEMP_M;HR;PRECIP
01/06/14 00:50:00;314.3;1.9;14.1;68.0;-99.9
01/06/14 01:50:00;322.0;1.6;13.3;68.9;-99.9
01/06/14 02:50:00;303.5;2.1;12.3;70.9;-99.9
01/06/14 03:50:00;302.4;1.6;11.6;73.1;-99.9
01/06/14 04:50:00;306.5;1.2;10.9;76.4;-99.9
01/06/14 05:50:00;317.1;0.8;12.6;71.5;-99.9
01/06/14 06:50:00;341.8;0.0;17.1;58.8;-99.9
01/06/14 07:50:00;264.6;1.2;21.8;44.9;-99.9
01/06/14 08:50:00;253.8;2.9;24.7;32.2;-99.9
01/06/14 09:50:00;254.6;3.7;26.7;27.7;-99.9
01/06/14 10:50:00;250.7;4.3;28.3;24.9;-99.9
01/06/14 11:50:00;248.5;5.3;29.1;22.6;-99.9
01/06/14 12:50:00;242.8;4.7;30.3;20.4;-99.9
01/06/14 13:50:00;260.7;4.9;31.3;17.4;-99.9
01/06/14 14:50:00;251.8;5.1;31.9;17.1;-99.9
01/06/14 15:50:00;258.1;4.6;32.4;15.3;-99.9
01/06/14 16:50:00;254.3;5.7;32.4;14.0;-99.9
01/06/14 17:50:00;252.5;4.6;32.0;14.1;-99.9
01/06/14 18:50:00;257.4;3.8;31.1;14.9;-99.9
01/06/14 19:50:00;135.8;4.2;26.0;41.2;-99.9
01/06/14 20:50:00;126.0;1.7;23.5;48.7;-99.9
01/06/14 21:50:00;302.8;0.7;21.6;53.9;-99.9
01/06/14 22:50:00;294.2;1.1;19.3;67.4;-99.9
01/06/14 23:50:00;308.5;1.0;17.5;72.4;-99.9"
cat(Lines, "\n", file = "data.txt")

library(zoo)
z <- read.zoo("data.txt", header = TRUE, sep = ";", na.strings = "-99.9", 
        tz = "", format = "%y/%m/%d %H:%M:%S")
# move last 12 points into following day
time(z)[13:24] <- time(z)[13:24] + 24 * 60 * 60
xlim <- as.POSIXct(c("2001-06-14 00:00:00", "2001-06-14 12:00:00"))

Here are the 3 ways to plot it:

1 - classic graphics using plot.zoo:

# Create manual axis since classic graphic's default is not so good.
# Axis might be ok for real data in which case manual axis setting can be omitted
plot(z$VEL_M, type = "p", xlab = "X", ylab = "Y", col = "blue", xlim = xlim,
    xaxt = "n")
xaxis <- seq(xlim[1], xlim[2], by = "hour")
axis(1, xaxis, as.POSIXlt(xaxis)$hour)

2 - lattice graphics using xyplot.zoo :

library(lattice)
xyplot(z$VEL_M, type = "p", xlab = "X", ylab = "Y", col = "blue", xlim = xlim)

3 - ggplot2 using qplot:

# unlike classic graphics and lattice graphics, zoo currently 
# does not have a specific interface but we can do this:
library(ggplot2)
qplot(time(z), z$VEL_M, xlab = "X", ylab = "Y") + 
    geom_point(colour = "blue") +
    scale_x_datetime(limits = xlim)

EDIT:

Have modified example in order to illustrate limiting the X axis.

Hi and thanks for your answer. I have tried the ggplot2 option and works fine for the whole data set but I can't make the graphic when trying to set x axis limits. I try `scale_x_date(limits = as.Date(c("2007-01-01","2007-01-31")),format = "%Y-%m-%d")` and then no point appears, x limits are well defined but any data. R says that "Removed 105192 rows containing missing values (geom_point)". Any idea? — pacomet, Oct 04 '11 at 08:35
Hi again. I've accepted the other answer as it helped me to understand about POSIXct date and time format buy yours it was also helpful. — pacomet, Oct 04 '11 at 09:55
@pacomet. Have modified example to illustrate limiting X axis. — G. Grothendieck, Oct 04 '11 at 13:50

R ggplot2 plotting hourly data

2 Answers2

Linked