R中数据框中条件的Sumproduct

Question

考虑以下数据框：

df <- data.frame(row_id = c("r1","r2","r3","r4","r1","r2","r3","r4"),
                 v1 = c(3,2,5,2,5,2,6,4),
                 v2 = c(4,3,5,3,7,4,6,7))

我想用 "row_id" 求和积。也就是说，对于带有 row_id 的行："r1" 我想进行以下计算：(3*4)+(5*7)。等等。

因此，我最终将得到以下矩阵：

df1 <- data.frame(row_id = c("r1","r2","r3","r4"),
                 v1 = c(47,14,61,34))

任何帮助将不胜感激。

谢谢。

Answer 1

library(dplyr)
df %>%
    mutate(p = Reduce("*", .[-1])) %>%
    group_by(row_id) %>%
    summarise(v = sum(p))

或

tapply(Reduce("*", df[-1]), df$row_id, sum)
#r1 r2 r3 r4 
#47 14 61 34

Answer 2

类似但略短：

dplyr::count(df, row_id, wt = v1*v2)

Answer 3

将 base R 与 split 和 %*%

结合使用

sapply(split(df[-1], df$row_id), function(x) x[,1] %*% x[,2])
# r1 r2 r3 r4 
#47 14 61 34

或者另一个选项是 rowsum 来自 base R

rowsum(with(df, v1 * v2), group = df$row_id)
#    [,1]
#r1   47
#r2   14
#r3   61
#r4   34

或使用data.table

library(data.table)
setDT(df)[, do.call(`%*%`, .SD), row_id]
#   row_id V1
#1:     r1 47
#2:     r2 14
#3:     r3 61
#4:     r4 34

Answer 4

使用 base R，我们还可以 transform 然后 aggregate

 aggregate(tot~row_id,transform(df,tot = v1*v2),sum)

  row_id tot
1     r1  47
2     r2  14
3     r3  61
4     r4  34

或者你也可以这样做：

c(by(df[-1],df[1],do.call,what = "%*%"))
r1 r2 r3 r4 
47 14 61 34

Answer 5

使用 dplyr:

library(dplyr)
df %>% group_by(row_id) %>% summarize(sum(v1*v2))

# which gives:
# A tibble: 4 x 2
  row_id `sum(v1 * v2)`
  <fct>           <dbl>
1 r1                 47
2 r2                 14
3 r3                 61
4 r4                 34

R中数据框中条件的Sumproduct

Sumproduct by condition in a data frame in R

r

vector

sumproduct