plotting monthly and yearwise weather data in r

Question

I am trying to develop a weather plot like that appears in weather data - something like.

I want to plot daily value (although average value can appear in circle). I am using ggplot2 as it need multifaceted (for each month and year).

st <- as.Date ("2009-1-1")
en <- as.Date ("2011-12-28")
date1 <- seq(st, en, "1 day")
year <- format(date1, "%Y")
month <- format (date1, "%b")
day <- as.numeric (format(date1, "%d"))

avgtm <- round (rnorm (length(date1), 50,5), 1)
maxtm <- avgtm + abs(rnorm (length (avgtm), 0, 5))
mintm <-  avgtm - abs(rnorm (length (avgtm), 0, 5))

myd <- data.frame ( year, month, day, avgtm, maxtm, mintm)
require(ggplot2)
qplot(day, avgtm, data = myd, geom = "line", col = "red") +
facet_grid(year ~ month) + theme_bw()

There is one major problem here, line will connect between months.

Each month is plotted to maximum (although one month can end in 28, leaving blank at the month).

Is there a smart way to achieve what I want to achieve. I tried ggplot2 but there might be other nice options.

Edit:

I am trying to add vertical line at the first day of month to demark the months. Here is I tried to find the first day of month:

 td = as.Date (seq(as.Date("2009/1/1"), as.Date("2011/12/28"), "months"))

I tried to use this to plot line:

qplot(date, avgtm, data = myd, geom = "line", col = "red") +
  facet_wrap(~year, scales='free_x', ncol=1, nrow=3) +

   geom_vline(xintercept=td, linetype="dotted") + theme_bw()

But running an error: Error : Invalid intercept type: should be a numeric vector, a function, or a name of a function

How can plot the vertical line with the date ?

Answer 1

There is a solution with panel.xblocks from latticeExtra:

st <- as.Date("2009-1-1")
en <- as.Date("2011-12-28")
date1 <- seq(st, en, "1 day")

avgtm <- round (rnorm (length(date1), 50,5), 1)

myd <- data.frame(date1, avgtm)

I define two functions to extract month and year values instead of including them in the data.frame. This approach is useful with panel.xblocks in the panel function of xyplot:

month <- function(x)format(x, '%m')
year <- function(x)format(x, '%Y')

I use year(date1) as conditioning variable to produce three panels. Each of these panels will display the time series for that year (panel.xyplot) and a sequence of contiguous blocks with alternating colors to highlight months (panel.xblocks). You should note that the y argument in panel.xblocks is the function month previously defined:

xyplot(avgtm ~ date1 | year(date1), data=myd,
       type='l', layout=c(1, 3),
       scales=list(x=list(relation='free')),
       xlab='', ylab='',
       panel=function(x, y, ...){
           panel.xblocks(x, month,
                         col = c("lightgray", "white"),
                         border = "darkgray")
           panel.xyplot(x, y, lwd = 1, col='black', ...)
           })

Answer 2

How about making a date column, then faceting on year only

myd$date <- as.Date(paste(myd$year, myd$month, myd$day), format='%Y %b %d')

qplot(date, avgtm, data = myd, geom = "line", col = "red") +
  facet_wrap(~year, scales='free_x', ncol=1, nrow=3)

You could add scales='free_x' to your plot as well, but will find it makes interpretation difficult.

By faceting on month and year you are telling the viewer and the plotting tool that the variables plotted are not continuous. This is incorrect as you've pointed out in your question. Thus, no faceting... You can add tick marks for each month or each day if you want.

library(scales)
qplot(date, avgtm, data = myd, geom = "line", col = "red") +
      facet_wrap(~year, scales='free_x', ncol=1, nrow=3) +
      scale_x_date(breaks=date_breaks("month"), labels=date_format("%b"))

Alternatively you could extract day of year and plot everything on one plot, coloring by year:

myd$doy <- format(myd$date, '%j')
p <- ggplot(myd, aes(x=doy, y=avgtm, color=year, group=year))

p + geom_line()

or

p + geom_smooth()