使用ddply汇总时如何添加列

Question

我的问题是用 ddply 函数总结 data.frame，例如以下。

该函数用于创建具有最大评级和相应公司的新数据框。缺少的是第一个数据帧中的相应 ID。

我试图调用 ID 变量，但这导致出现错误消息。我对最高评分对应的ID感兴趣

非常感谢您的提前帮助！

dat <- data.frame(ID = c("A11", "A12", "A21","A22","A23","A31"), 
              company =  c("CompA","CompA","CompB","CompB","CompB","CompC"),
              rating = c(1,4,2,5,3,4)
              )

company  ID ratingMax
1   CompA A11         1
2   CompA A12         4
3   CompB A21         2
4   CompB A22         5
5   CompB A23         3             
6   CompC A31         4

library(plyr)
ddply(dat, "company", summarise, ratingMax = max(rating))

company ratingMax
1   CompA         4
2   CompB         5
3   CompC         4

ddply(dat, "company", summarise, ratingMax = max(rating), ID = ID)
Error: length(rows) == 1 is not TRUE

Answer 1

你可以试试

 library(plyr) 
 ddply(dat, "company", summarise, ratingMax = max(rating),
             ID = ID[which.max(rating)])
 #  company ratingMax  ID
 #1   CompA         4 A12
 #2   CompB         5 A22
 #3   CompC         4 A31

或使用dplyr

 library(dplyr)
 dat %>% 
      group_by(company) %>% 
      summarise(ratingMax=max(rating), ID=ID[which.max(rating)])
 #  company ratingMax  ID
 #1   CompA         4 A12
 #2   CompB         5 A22
 #3   CompC         4 A31

或者您可以使用 filter

   dat %>% 
       group_by(company) %>% 
       filter(row_number() %in% which.max(rating))

或者按照@docendo discimus

的建议使用slice（这样会更快更紧凑）

  dat %>% 
      group_by(company) %>%
      slice(which.max(rating))

Answer 2

这是一个快速 data.table 解决方案，它可以让您无需手动命名列（以防您要显示更多列）

library(data.table)
setDT(dat)[, .SD[which.max(rating)], by = company]
#    company  ID rating
# 1:   CompA A12      4
# 2:   CompB A22      5
# 3:   CompC A31      4

使用ddply汇总时如何添加列

How to add column when summarising with ddply

r

plyr

dataframe