R：如何对按因子分组的列求和？ [英] R: how to sum columns grouped by a factor?

问题描述

如果我有这样的表：

user,v1,v2,v3
a,1,0,0
a,1,0,1
b,1,0,0
b,2,0,3
c,1,1,1

如何将其变成这个？

user,v1,v2,v3
a,2,0,1
b,3,0,3
c,1,1,1

推荐答案

您可以为此使用 dplyr ：

library(dplyr)
df = data.frame(
  user = c("a", "a", "b", "b", "c"),
  v1   = c(1, 1, 1, 2, 1),
  v2   = c(0, 0, 0, 0, 1),
  v3   = c(0, 1, 0, 3, 1))

group_by(df, user) %>% 
summarize(v1_sum = sum(v1),
          v2_sum = sum(v2),
          v3_sum = sum(v3))      

如果您不熟悉％>％表示法，则基本上就像是bash的管道。它从 group_by（）中获取输出，并将其放入 summarize（）中。这样可以完成相同的事情：

If you're not familiar with the %>% notation, it is basically like piping from bash. It takes the output from group_by() and puts it into summarize(). The same thing would be accomplished this way:

by_user = group_by(df, user)
df_summarized = summarize(by_user, 
                          v1_sum = sum(v1),
                          v2_sum = sum(v2),
                          v3_sum = sum(v3))  

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