将24h转换为AM / PM格式

Question

I have a numeric variable, to be plotted on the x-axis, containing digits from 0 to 23. I a) need to convert these hours into Date objects in order to visualize them in a ggplot , and I b) want to have the x-axis display these numbers in am/pm format.

So far I have:

library("ggplot2")
library(scales)
Sys.setlocale(category = "LC_ALL", locale = "English")
# data
hod <- structure(list(h = c(0L, 0L, 0L, 0L, 0L, 1L, 1L, 1L, 1L, 1L), 
t = c(NA, 2L, 4L, 1L, 3L, NA, 2L, 4L, 1L, 3L), n = c(226L, 
226L, 226L, 226L, 226L, 226L, 226L, 226L, 226L, 226L), mean = c(4.52654867256637, 
33.6769911504425, 6.34513274336283, 30.3672566371681, 0.309734513274336, 
2.84513274336283, 20.0088495575221, 3.38938053097345, 17.7787610619469, 
0.101769911504425), std = c(2.74131025125736, 13.4781731703065, 
3.0316031901839, 10.9165210711549, 0.603524251739029, 2.25142987605743, 
10.9354466064168, 2.27892859595505, 8.76056582129717, 0.33032092222724
)), .Names = c("h", "t", "n", "mean", "std"), row.names = c(NA, 
10L), class = "data.frame")



ggplot(hod, aes(x=h, y=mean, colour=as.factor(t))) + 
geom_line(size = .1) +
geom_point() +
theme_minimal()

hod$h would actually continue up until 23 , but I only included 0 and 1 for reasons of space. What I want is the x-axis to show 6am, 9am, 12am, 3pm, 6pm, 9pm, 12pm , or something like this. Can't be that hard can it? I tried experimenting with scale_x_date which requires a Date object, but I failed because I didn't know how to deal with the origin - there isn't any origin just hours!

Answer 1

You could use strftime to format times as you require and use this as the x aesthetic. You will then have to also use a grouping aesthetic. We use lubridate to make it easy to work with hours. Try this:

require(lubridate)    
hod$time <- tolower( strftime( Sys.Date()+hours(hod$h) , "%I %p" ) )
# [1] "12 am" "12 am" "12 am" "12 am" "12 am" "01 am" "01 am" "01 am" "01 am" "01 am"

ggplot(hod, aes( x = time , y=mean, colour=as.factor(t) , group = t ) ) + 
geom_line(size = .1) +
geom_point()

Answer 2

ggplot(hod, aes( x = h , y=mean, colour=as.factor(t))) + 
  geom_line(size = .1) +
  geom_point() +
  scale_x_continuous(limits=c(0,24),
                     breaks=0:12*2,
                     labels=c(paste(0:5*2,"am"),
                              "12 pm",
                              paste(7:11*2-12,"pm"), 
                              "0 am"))