Jeremy Yoder’s code for a simple Gantt chart on the Molecular Ecologist blog uses geom_line and gather to prepare the data structure. I like using geom_linerange and a coord_flip, which lets you use start and end columns directly without pivoting.

Here is a very serious data frame of activities:

# A tibble: 6 x 4
  activity       category        start               end                
                                                  
1 Clean house    preparations    2020-07-01 00:00:00 2020-07-03 00:00:00
2 Pack bags      preparations    2020-07-05 10:00:00 2020-07-05 17:00:00
3 Run to train   travel          2020-07-05 17:00:00 2020-07-05 17:15:00
4 Sleep on train travel          2020-07-05 17:15:00 2020-07-06 08:00:00
5 Procrastinate  procrastination 2020-07-01 00:00:00 2020-07-05 00:00:00
6 Sleep          vacation        2020-07-06 08:00:00 2020-07-09 00:00:00

And here is the code:

library(ggplot2)
library(readr)

activities <- read_csv("activities.csv")

## Set factor level to order the activities on the plot
activities$activity <- factor(activities$activity,
                              levels = activities$activity[nrow(activities):1])
    
plot_gantt <- qplot(ymin = start,
                    ymax = end,
                    x = activity,
                    colour = category,
                    geom = "linerange",
                    data = activities,
                    size = I(5)) +
    scale_colour_manual(values = c("black", "grey", "purple", "yellow")) +
    coord_flip() +
    theme_bw() +
    theme(panel.grid = element_blank()) +
    xlab("") +
    ylab("") +
    ggtitle("Vacation planning")