R 将日期组转换为连续整数

我有下面的示例数据集，我想将每个日期组转换为一个整数，其中最早的日期从1开始，并且对于每个新的日期组连续增长。任何帮助都将不胜感激

dateA = c("5/8/2020","5/8/2020", "5/8/2020", "5/9/2020","5/9/2020", "5/9/2020", "5/9/2020", "5/10/2020","5/10/2020", "5/10/2020", "5/11/2020")
varA = c(2,3,4,9,10,11,12,20,21,22,55)
data = data.frame(dateA,varA)

当前尝试

library(dplyr)
data = data %>%
  mutate(varA = as.integer(factor(dateA)))

      dateA varA
1   5/8/2020    3
2   5/8/2020    3
3   5/8/2020    3
4   5/9/2020    4
5   5/9/2020    4
6   5/9/2020    4
7   5/9/2020    4
8  5/10/2020    1
9  5/10/2020    1
10 5/10/2020    1
11 5/11/2020    2

---

一个选项是

match

library(dplyr)
 data %>% mutate(varA = match(dateA, unique(dateA)))

或具有指定的

水平的
系数

data %>%
    mutate(varA = as.integer(factor(dateA, levels = unique(dateA)))

data %>%
    mutate(varA = as.integer(factor(dateA, levels = unique(dateA)))