ggplot2反转日期类型Y轴报错：仅支持POSIXct类对象

问题描述 #

复现旧版社区方案中反转日期类型Y轴的代码时，出现报错：

Error: Invalid input: time_trans works with objects of class POSIXct only

执行代码与旧方案一致，但当前环境为：R版本4.2.2，ggplot2版本3.4.0。

原尝试代码：

MyData <- structure(list(Date = structure(c(1492979809.99827, 1492602845.68722, 1493093428.90318, 1492605578.0691, 1492961342.65056, 1492771976.83545, 1493020588.88485, 1493057018.85104, 1492852011.23873, 1492855996.55059), class = c("POSIXct", "POSIXt")), Value = c(4.52885504579172, 6.0024610790424, 8.96430060034618, 7.06435370026156, 5.08460514713079, 3.47828012891114, 6.29844291834161, 0.898315710946918, 1.44857675535604, 5.74641009094194)), .Names = c("Date", "Value"), row.names = c(NA, -10L), class = "data.frame")

library(ggplot2)
library(scales)

c_trans <- function(a, b, breaks = b$breaks, format = b$format) {
  a <- as.trans(a)
  b <- as.trans(b)
  
  name <- paste(a$name, b$name, sep = "-")
  
  trans <- function(x) a$trans(b$trans(x))
  inv <- function(x) b$inverse(a$inverse(x))
  
  trans_new(name, trans, inverse = inv, breaks = breaks, format=format)

}

rev_date <- c_trans("reverse", "time")

ggplot(MyData, aes(x=Value, y=Date)) +
  geom_point() + 
  scale_y_continuous(trans = rev_date)

报错原因 #

这是版本兼容性问题：ggplot2 3.3.0及后续版本对轴转换逻辑做了调整，原方案用scale_y_continuous处理POSIXct类型轴时，会导致数据在转换过程中丢失POSIXct类属性，触发time_trans的类型检查报错。

修复方案 #

无需自定义转换函数，直接使用ggplot2内置的scale_y_datetime配合reverse转换即可，代码如下：

MyData <- structure(list(Date = structure(c(1492979809.99827, 1492602845.68722, 1493093428.90318, 1492605578.0691, 1492961342.65056, 1492771976.83545, 1493020588.88485, 1493057018.85104, 1492852011.23873, 1492855996.55059), class = c("POSIXct", "POSIXt")), Value = c(4.52885504579172, 6.0024610790424, 8.96430060034618, 7.06435370026156, 5.08460514713079, 3.47828012891114, 6.29844291834161, 0.898315710946918, 1.44857675535604, 5.74641009094194)), .Names = c("Date", "Value"), row.names = c(NA, -10L), class = "data.frame")

library(ggplot2)

ggplot(MyData, aes(x=Value, y=Date)) +
  geom_point() + 
  scale_y_datetime(trans = "reverse")

方案说明 #

• scale_y_datetime专门匹配POSIXct类型的轴，避免数据转换时丢失类属性
• 内置的reverse转换已原生支持datetime轴，无需自定义组合转换函数

内容的提问来源于stack exchange，提问作者VinayShastri