How do I plot time (HH:MM:SS) in X axis in R

Question

I have tried to read through stackoverflow, blogs, books etc but have been unable to find the answer on plotting time in the x-axis in the following format(HH:MM:SS.000) in R and another quantity on the y-axis. I have the following dataset:

Time             EcNo
12:54:09.000    -14.47
12:54:10.000    -17.96
12:54:11.000    -15.97
12:54:12.000    -14.61
12:54:13.000    -12.68
12:54:14.000    -10.73
12:54:15.000    -10.54
12:54:16.000    -11.62
12:54:17.000    -12.49
12:54:18.000    -11.12

How would I plot EcNo on Yaxis vs Time(x axis) in the format HH:MM:SS.000 as shown above.

I honestly would appreciate some help. many thanks

Answer 1

You may also try ggplot:

library(ggplot2)
df$time <- as.POSIXct(strptime(df$Time, format="%H:%M:%S"))

# Automatic scale selection
ggplot(data = df, aes(x = time, y = EcNo)) + geom_point()

scale_x_datetime is a ggplot function, but for the nice arguments date_breaks, and date_format you need package scales:

library(scales)

ggplot(data = df, aes(x = time, y = EcNo)) + geom_point() +
  scale_x_datetime(breaks = date_breaks("1 sec"), labels = date_format("%S"))

ggplot(data = df, aes(x = time, y = EcNo)) + geom_point() +
  scale_x_datetime(breaks = date_breaks("1 sec"), labels = date_format("%OS3"))

ggplot(data = df, aes(x = time, y = EcNo)) + geom_point() +
  scale_x_datetime(breaks = date_breaks("4 sec"), labels = date_format("%M:%S"))

Answer 2

plot(strptime(dta$Time, format="%H:%M:%S"), dta$EcNo, xaxt="n")
axis(1, at=as.numeric(strptime(dta$Time, format="%H:%M:%S")), 
       labels=strftime( strptime(dta$Time, format="%H:%M:%S"),format="%H:%M:%S"))

Answer 3

df <- data.frame(
  Time=c('12:54:09.000','12:54:10.000','12:54:11.000','12:54:12.000','12:54:13.000','12:54:14.000','12:54:15.000','12:54:16.000','12:54:17.000','12:54:18.000'),
  EcNo=c(-14.47,-17.96,-15.97,-14.61,-12.68,-10.73,-10.54,-11.62,-12.49,-11.12)
)

op <- options(digits.secs=3)
plot(as.POSIXct(df$Time,format="%H:%M:%OS"),df$EcNo,xaxt="n")
axis.POSIXct(1, as.POSIXct(df$Time,format="%H:%M:%OS"), format="%H:%M:%OS")