基于两列对数据框中的行进行求和[重复]

我想添加一列的值，将它们按两列分组。我找到了如何在一列上执行此操作，但无法弄清楚如何在两列上执行此操作。 例如，如果我有以下数据框：

x=c("a","a", "b", "b","c", "c","a","a","b","b","c","c", "a", "a","b","b", "c", "c") 
y=c(1:18) 
q=c("M","M","M", "M","M","M","W","W","W","W","W","W","F","F","F","F","F","F")
df<-data.frame(x,y,q)

我想在 x 和 q 之间添加 y 列中的值，这样我就有一个像这样的新数据框

x=c("a","a", "b", "b","c", "c","a","a","b","b","c","c", "a", "a","b","b", "c", "c") 
y=c(3,7,11,15,19,23,27,31,35) 
q=c("M","M","M","W","W","W","F","F","F")
d<-data.frame(x,y,q)

您有多种选择：

1: Base R

aggregate(y ~ x + q, df, sum)

2:数据表

library(data.table)
setDT(df)[, .(sumy = sum(y)), by = .(x, q)]

# when you want to summarise several columns:
setDT(df)[, lapply(.SD, sum), by = .(x, q)]

3: dplyr

library(dplyr)
df %>% group_by(x, q) %>% summarise(sumy = sum(y))

# when you want to summarise several columns:
df %>% group_by(x, q) %>% summarise_each(funs(sum))

所有这些都应该给你相同的结果（尽管顺序不同）。例如，data.table输出看起来像这样：

   x q  y
1: a M  3
2: b M  7
3: c M 11
4: a W 15
5: b W 19
6: c W 23
7: a F 27
8: b F 31
9: c F 35