plotting only time using ggplot2

Question

I have a data frame like this:

 head(yy)
    Team       Date STime ETime
1    A 2012-03-06 07:03 10:13
2    A 2012-03-06 07:03 10:13
3    A 2012-03-06 07:03 10:13
4    A 2012-03-06 07:03 10:13
5    A 2012-03-06 07:03 10:13
6    A 2012-03-06 07:03 10:13

dput(yy)

dput(yy)
structure(list(Team = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = "A", class = "factor"), 
Date = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = "2012-03-06", class = "factor"), 
STime = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = "07:03", class = "factor"), 
ETime = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = "10:13", class = "factor")), .Names = c("Team", 
"Date", "STime", "ETime"), class = "data.frame", row.names = c(NA, 
-50L))

I like to see the y-axis from 00:00 23:59 in 2 hours increment and be able to draw a red line on STime value.

I have somthing like this but it does not look right:

ggplot(yy, aes(Date, ETime, group="Team")) + geom_jitter(size=0.05) + facet_wrap( ~ Team) + geom_hline(yintercept=yy$Stime, colour="red", size=2)

how would you do this in ggplot2? Can somebody give me pointers/start me in the right direction?

Regards,

Answer 1

You have to format your times into actual times. Right now they are factors (Check your data frame with str(yy)). When ETime is plotted, the single time is plotted as 1 and labeled "10:13." So, the solution below first converts the string "10:13" into a time (strptime) then converts it to POSIXct, or seconds since an origin (1/1/1970).

library(ggplot2); library(scales)

#Convert date string into POSIXct format
yy$STime <- as.POSIXct(strptime(yy$STime, format = "%H:%M", tz = "UTC"))
yy$ETime <- as.POSIXct(strptime(yy$ETime, format = "%H:%M", tz = "UTC"))

#Define y-axis limits
lims <- as.POSIXct(strptime(c("0:00","23:59"), format = "%H:%M", tz= "UTC"))    

ggplot(yy, aes(Date, ETime, group="Team")) + geom_jitter(size=1) + facet_wrap( ~ Team) + 
  geom_hline(data = yy, aes(yintercept= as.numeric(STime)), colour="red", size=2) + 
  scale_y_datetime(limits =lims, breaks=date_breaks("2 hour"),
                   labels=date_format("%H:%M", tz = "UTC") )

Note on geom_line to date axis.

Pay attention to your timezones too. Otherwise R/ggplot will format things according to your local time zone.