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rtimestampaxis-labels

Data with timestamp in format "dd.mm.yyy HH:MM:SS" and plotting

I have data with one column of being timestamp in format dd.mm.yyyy HH:MM:SS. This is how the data looks like:

> data$TimeStamp [1] "14.3.2017 10:00:00" "14.3.2017 10:00:01" "14.3.2017 10:00:02" "14.3.2017 10:00:03" "14.3.2017 10:00:04" "14.3.2017 10:00:05"

My goal is to produce plots with timestamps on x-axis with only time HH:MM:SS as labels but the time span may be longer than one day.

So for example my x-axis labels could look like this at each tick with one hour intervals:

22:00:00     23:00:00     00:00:00     01:00:00     02:00:00

I have thought about splitting the character string into date and time and convert time into seconds before plotting but I am willing to hear any alternative paths to do this since I probably will have issues with automatically assigning axis labels properly.

Solution

  • Given

    df <- data.frame(
  x=Sys.time()+runif(100, 1, 60*60*24*2),
  y=runif(100))
df$x <- as.character(df$x)
str(df)
# 'data.frame': 100 obs. of  2 variables:
#  $ x: chr  "2017-06-13 18:33:35" "2017-06-14 11:51:49" "2017-06-12 21:51:10" ...
#  $ y: num  0.634 0.738 0.334 0.885 0.461 ...

    you could define a sort of labeling function

    f <- function(x) as.POSIXct(levels(cut(x, breaks = "2 hours")))

    and then do

    df$x <- as.POSIXct(df$x)
plot(y~x, df, xaxt="n")
with(df, axis(1, at=f(x), labels=format(f(x), "%H:%M:%S")))