ggplot 在使用数字 x 值的同时向 x 轴添加日期标签

Question

我想重现以下情节，但我想每 4 个月添加一次日期标签而不是数字。

我必须将 date_time 值转换为数字才能绘制

annotate("rect")

，因为我希望它将矩形的长度延伸到绘图的边缘，类似于

geom_hline

。我发现

annotate

方法最快。我现在有一个问题，因为我想在 x 轴上使用日期标签而不是数字。

我尝试过使用

scale_x_continuous

，但这花了太长时间并且似乎不起作用。

感谢您的帮助。

# Reproducible data
set.seed(123)

start_date_time <- as.POSIXct("2023-07-01 00:00:00")
end_date_time <- as.POSIXct("2023-07-02 00:00:00")
date_time <- seq(from = start_date_time, to = end_date_time, by = "15 min")

depth <- runif(length(date_time), min = 0, max = 0.5)

df <- data.frame(date_time = date_time, depth = depth)

df$N_dt <- as.numeric(df$date_time)
x_point <- min(df$N_dt)

full_level <- 0.4
pipe_bottom <- 0.15
pipe_top <- 0.35
pipe <- 0.25

df %>%
  ggplot(aes(x = N_dt,
             y = depth)) +
  geom_line(size = 0.25) +
  labs(x = "Date", 
       y = "Water level (m)") +
  geom_hline(yintercept = full_level, linetype = 'dashed', 
             color = 'black') +
  annotate("text", x = x_point, y = (full_level + 0.03),
           label = "Full level", size = 8 / .pt) +
  annotate("text", x = x_point, y = pipe,
           label = "Pipe", size = 8 / .pt) +
  annotate("rect", xmin = -Inf, xmax = Inf,
           ymin = pipe_bottom, ymax = pipe_top, alpha = .1) +
  theme_classic() +
  theme(
    plot.title = element_blank(),
    axis.text = element_text(size = 8),
    axis.title = element_text(size = 8.5),
    legend.title = element_blank(),
    legend.position = "top",
    panel.border = element_rect(color = "black", fill = NA)
  )

Answer 1

您可以使用

labels

的

scale_x_continuous

参数将数字转换回日期时间。

df %>%
  ggplot(aes(x = N_dt,
             y = depth)) +
  geom_line(size = 0.25) +
  labs(y = "Water level (m)") +
  scale_x_continuous(labels = ~ format(as.POSIXct(.x, origin = '1970-01-01'),
                                       '%d %b %Y %H:%M')) +
  geom_hline(yintercept = full_level, linetype = 'dashed', 
             color = 'black') +
  annotate("text", x = x_point, y = (full_level + 0.03),
           label = "Full level", size = 8 / .pt) +
  annotate("text", x = x_point, y = pipe,
           label = "Pipe", size = 8 / .pt) +
  annotate("rect", xmin = -Inf, xmax = Inf,
           ymin = pipe_bottom, ymax = pipe_top, alpha = .1) +
  theme_classic() +
  theme(
    plot.title = element_blank(),
    axis.text = element_text(size = 8),
    axis.title = element_text(size = 8.5),
    legend.title = element_blank(),
    legend.position = "top",
    panel.border = element_rect(color = "black", fill = NA)
  )

Answer 2

一种选择是坚持日期时间，这样您就可以通过

scale_x_datetime

轻松设置所需的日期休息时间。为了使这项工作与您的矩形一起工作，我直接根据您的日期范围设置

xmin

和

xmax

。这一步的棘手部分是，这样做我们必须考虑扩展：

library(ggplot2)

# Set the range for the rects
range_rect <- range(df$date_time)
# Add some expansion
range_rect <- range_rect + .1 * c(-1, 1) * diff(range_rect)

x_point <- min(df$date_time)

df %>%
  ggplot(aes(
    x = date_time,
    y = depth
  )) +
  geom_line(size = 0.25) +
  labs(
    x = "Date",
    y = "Water level (m)"
  ) +
  geom_hline(
    yintercept = full_level, linetype = "dashed",
    color = "black"
  ) +
  annotate("text",
    x = x_point, y = (full_level + 0.03),
    label = "Full level", size = 8 / .pt
  ) +
  annotate("text",
    x = x_point, y = pipe,
    label = "Pipe", size = 8 / .pt
  ) +
  annotate("rect",
    xmin = range_rect[[1]], xmax = range_rect[[2]],
    ymin = pipe_bottom, ymax = pipe_top, alpha = .1
  ) +
  # As we already added the expansion via range_rect,
  # set it to zero for the scale
  scale_x_datetime(
    expand = c(0, 0)
  ) +
  theme_classic() +
  theme(
    plot.title = element_blank(),
    axis.text = element_text(size = 8),
    axis.title = element_text(size = 8.5),
    legend.title = element_blank(),
    legend.position = "top",
    panel.border = element_rect(color = "black", fill = NA)
  )