Question

I have a frame with temperature data and the time it was read. It looks like this:

> head(dx)
                       t Temp
1218 2012-11-13 00:01:15   79
1219 2012-11-13 00:07:19   80
1220 2012-11-13 00:15:19   78
1221 2012-11-13 00:22:57   82
1222 2012-11-13 00:30:25   78
1223 2012-11-13 00:43:19   75
...
> tail(dx)
                       t Temp
2240 2012-11-17 13:37:19  106
2241 2012-11-17 13:43:23  106
2242 2012-11-17 13:49:25  106
2243 2012-11-17 13:55:25  106
2244 2012-11-17 14:00:00  107
2245 2012-11-17 14:06:23  107

I want to show it in a graph with ticks for every day. I use

plot(dx$t, dx$Temp/10)

to display the data, which works well, but the ticks shown on x-axis are too few. I would like to show one tick for each day. What’s the best way to do it? There are many questions with slightly different requests, so I got lost. If this questions was asked already I would appreciate a link.

Answer 1

Here’s one way to achieve this with base plots, but as Justin suggested, you could also look into packages that offer additional flexibility for plotting date objects, such as zoo and xts.

t <- seq(ISOdatetime(2012,1,1,11,10,25), ISOdatetime(2012,03,31,11,10,25), "hours")
dx <- data.frame(t=t, Temp=runif(length(t)))
plot(dx$t, dx$Temp/10, xaxt='n')
axis(1, at=as.POSIXct(unique(format(dx$t, '%Y-%m-%d')), format='%Y-%m-%d'),
     labels=unique(format(dx$t, '%Y-%m-%d')))