如何将甘特图（Gantt Chart）Y轴地点按字母顺序排序？

你尝试生成Y轴地点按字母顺序排列的甘特图但未成功，以下是针对你提供的代码和数据的解决方案：

要让ggplot的Y轴按字母排序，核心是把location列转换为因子类型并指定排序后的水平——因为ggplot对离散轴的排序依据是因子的水平顺序，而非数据框的行顺序（你之前用arrange只是调整了数据行的顺序，不影响轴的排序规则）。

修改后的完整代码 #

# 加载所需包
library(readxl)
library(reshape2)
library(dplyr)
library(ggplot2)
library(lubridate)

# 使用你提供的数据子集测试（实际使用时替换为read_excel("2025-05-07_gantt_chart.xlsx")）
gantt <- structure(list(location = c("Hebron GBS", "Hibernia GBS", "SeaRose FPSO", 
"bdv", "Holyrood Thermal Generating station", "bdv", "Soldier's pond", 
"bdv", "bdv", "bdv"), year = c("2019", "2019", "2019", "2019", 
"2019", "2019", "2019", "2019", "2019", "2019"), `start date` = structure(c(1567296000, 
1567296000, 1567296000, 1569369600, 1569801600, 1569974400, 1569974400, 
1570233600, 1570406400, 1570665600), tzone = "UTC", class = c("POSIXct", 
"POSIXt")), `end date` = structure(c(1572480000, 1572480000, 
1572480000, 1569715200, 1572393600, 1570060800, 1572393600, 1570320000, 
1570492800, 1570752000), tzone = "UTC", class = c("POSIXct", 
"POSIXt")), ...5 = c("FALSE", "FALSE", "FALSE", "FALSE", "FALSE", 
"only 1 day", "FALSE", "only 1 day", "only 1 day", "only 1 day"
)), row.names = c(NA, -10L), class = c("tbl_df", "tbl", "data.frame"
))

# 生成row_id
gantt$row_id <- seq(1,nrow(gantt))

# 处理日期并转换数据格式
mgantt <- melt(gantt, measure.vars = c("start date", "end date"))
mgantt$yday <- yday(mgantt$value)

# 关键步骤：按字母顺序排序地点，转换为因子
sorted_locations <- sort(unique(mgantt$location))
mgantt$location <- factor(mgantt$location, levels = sorted_locations)

# 绘图
ggplot(mgantt,
       aes(x = yday, 
           y = location,
           group = row_id)) +   
  geom_line(linewidth = 4) +
  facet_wrap(~year) +
  labs(title = NULL,
       x = "Julian date",
       y = NULL) +
  theme(panel.grid.minor = element_line(colour="white", linewidth = 0.5),
        legend.position="right",
        plot.title = element_text(hjust = 0.5))

关键逻辑说明 #

• sort(unique(mgantt$location))：提取所有不重复的地点名称，默认按字母升序排列（若需要降序，可添加参数decreasing = TRUE）
• factor(mgantt$location, levels = sorted_locations)：将location列转换为因子类型，并强制指定水平顺序，ggplot绘图时会严格遵循该顺序渲染Y轴

内容的提问来源于stack exchange，提问作者Fiona