在R语言中如何按组对行求和？合并相同物料与日期的行

需求：将数据集中**Item（物料）和Date（日期）**相同的行合并，对Quantity列的值求和，同时保留Description列（相同分组下该列值一致）。

原始数据集 #

library(tibble)
df <- tibble::tribble(
     ~Item,        ~Date,   ~Description, ~Quantity,
     "Saw", "01/02/2020",      "outdoor",        2L,
     "Saw", "01/02/2020",      "outdoor",        3L,
     "Saw", "01/04/2020",      "outdoor",        4L,
   "nails", "01/02/2020", "construction",        2L,
   "nails", "01/04/2020", "construction",        3L,
   "nails", "01/06/2020", "construction",        4L,
  "hammer", "01/01/2020",         "home",        1L,
  "hammer", "01/01/2020",         "home",        2L,
  "hammer", "01/01/2020",         "home",        3L
)

解决方案1：使用dplyr包 #

这是R中常用的tidyverse风格操作，通过分组后聚合实现：

library(dplyr)
df_agg <- df %>%
  group_by(Item, Date, Description) %>%
  summarize(Quantity = sum(Quantity), .groups = "drop")

• group_by(Item, Date, Description)：按物料、日期、描述分组（相同物料+日期的描述一致，加入分组可直接保留该列）
• summarize(Quantity = sum(Quantity))：对每组的数量求和
• .groups = "drop"：取消分组状态，返回普通数据框

解决方案2：使用data.table包 #

如果处理大数据集，data.table的运行效率更高：

library(data.table)
setDT(df)
df_agg <- df[, .(Quantity = sum(Quantity)), by = .(Item, Date, Description)]

最终结果 #

运行上述任意代码后，得到的结果与期望一致：

tibble::tribble(
     ~Item,        ~Date,   ~Description, ~Quantity,
     "Saw", "01/02/2020",      "outdoor",        5L,
     "Saw", "01/04/2020",      "outdoor",        4L,
   "nails", "01/02/2020", "construction",        2L,
   "nails", "01/04/2020", "construction",        3L,
   "nails", "01/06/2020", "construction",        4L,
  "hammer", "01/01/2020",         "home",        6L
)

内容的提问来源于stack exchange，提问作者kaza