如何使用ggplot2缩放轴的时间间隔？

Question

说我想绘制一堆时间间隔的直方图：

library(ggplot2)
library(dplyr)

# Generate 1000 random time difftime values
set.seed(919)
center <- as.POSIXct(as.Date("2014-12-18"))
df <- data.frame(
    center, 
    noise = center + rnorm(1000, mean = 86400, sd = 86400 * 3)
    ) %>%
  mutate(diff = center - noise)

# Plot histogram of the difftime values -- 
# coerce to numeric, because otherwise it won't plot
qplot(data = df, x = as.numeric(diff), geom = "histogram")

我得到这个情节：

有没有办法将x轴更改为合理的日期时间值？ （也就是说，我希望将86400标记为＆＃34; 1天＆＃34;， - 86400标记为＆＃34; - 1天＆＃34;等）我可以手动执行此操作通过设置中断和标签，但我希望ggplot能够自动处理difftime值。

Answer 1

您可以使用difftime()并使用days作为单位，而不是减去日期。

library(ggplot2)
library(dplyr)

# Generate 1000 random time difftime values
set.seed(919)
center <- as.POSIXct(as.Date("2014-12-18"))
df <- data.frame(
    center, 
    noise = center + rnorm(1000, mean = 86400, sd = 86400 * 3)
    ) %>%
  mutate(diff = difftime(center, noise, unit = "days"))

# Plot histogram of the difftime values -- 
# coerce to numeric, because otherwise it won't plot
qplot(data = df, x = as.numeric(diff), geom = "histogram") +
  xlab("Days") + ylab("Count")