r - 如何根据多个条件对行求和 - R？

Question

这个问题已经有答案了:

How to sum a variable by group (18 个回答)

已关闭 8 年前。

我有一个数据框，其中包含样地 ID (plotID)、树种代码 (species) 和覆盖值 (cover)。您可以看到其中一张图中有多个树种记录。如果每个图中存在重复的“物种”行，如何对“覆盖”字段求和？

例如，这里是一些示例数据:

# Sample Data
plotID = c( "SUF200001035014", "SUF200001035014", "SUF200001035014", "SUF200001035014", "SUF200001035014", "SUF200046012040",
       "SUF200046012040", "SUF200046012040", "SUF200046012040", "SUF200046012040", "SUF200046012040", "SUF200046012040")
species = c("ABBA",  "BEPA",  "PIBA2", "PIMA",  "PIRE",  "PIBA2", "PIBA2", "PIMA",  "PIMA",  "PIRE",  "POTR5", "POTR5")
cover = c(26.893939,  5.681818,  9.469697, 16.287879,  1.893939, 16.287879,  4.166667, 10.984848, 16.666667, 11.363636, 18.181818,
          13.257576)
df_original = data.frame(plotID, species, cover)

这是预期的输出:

# Intended Output
plotID2 = c( "SUF200001035014", "SUF200001035014", "SUF200001035014", "SUF200001035014", "SUF200001035014", "SUF200046012040",
            "SUF200046012040", "SUF200046012040", "SUF200046012040")
species2 = c("ABBA",  "BEPA",  "PIBA2", "PIMA",  "PIRE",  "PIBA2", "PIMA",  "PIRE",  "POTR5")
cover2 = c(26.893939,  5.681818,  9.469697, 16.287879,  1.893939, 20.454546, 18.651515, 11.363636, 31.439394)
df_intended_output = data.frame(plotID2, species2, cover2)

Answer 1

轻松使用聚合

aggregate(cover~species+plotID, data=df_original, FUN=sum) 

使用data.table更容易

as.data.table(df_original)[, sum(cover), by = .(plotID, species)]