Question

我有一个数据帧df1

df1<- data.frame(ID = c("A","B","A","A","B"),CLASS = c(1,1,2,1,4))
 ID CLASS
1  A     1
2  B     1
3  A     2
4  A     1
5  B     4

以及另外两个数据帧A和B

   > A<- data.frame(CLASS = c(1,2,3), DESCRIPTION = c("Unknown", "Tall", "Short"))
  CLASS DESCRIPTION
1     1     Unknown
2     2        Tall
3     3       Short

> B <- data.frame(CLASS = c(1,2,3,4), DESCRIPTION = c("Big", "Small", "Medium", "Very Big"))
  CLASS DESCRIPTION
1     1         Big
2     2       Small
3     3      Medium
4     4    Very Big

我想根据df1的ID和类来合并这三个数据帧，使其具有以下内容：

      ID CLASS DESCRIPTION
1  A     1     Unknown
2  B     1         Big
3  A     2        Tall
4  A     1     Unknown
5  B     4    Very Big

我知道我可以将其合并为df1 <- merge(df1, A, by = "CLASS")，但是我找不到找到添加条件（也可能是“如果”太多的方法）以根据ID合并B的方法。我需要一种有效的方法来完成此操作，因为我将其应用于超过200万行。

Answer 1

将ID变量添加到A和B，rbind A和B中，并使用ID和CLASS至merge：

A$ID = 'A'
B$ID = 'B'

AB <- rbind(A, B)

merge(df1, AB, by = c('ID', 'CLASS'))

  ID CLASS DESCRIPTION
1  A     1     Unknown
2  A     1     Unknown
3  A     2        Tall
4  B     1         Big
5  B     4    Very Big

我建议在创建数据时使用stringsAsFactors = FALSE：

df1 <- data.frame(ID = c("A","B","A","A","B"),CLASS = c(1,1,2,1,4),
                  stringsAsFactors = FALSE)
A <- data.frame(CLASS = c(1,2,3), 
                DESCRIPTION = c("Unknown", "Tall", "Short"),
                stringsAsFactors = FALSE)
B <- data.frame(CLASS = c(1,2,3,4), 
                DESCRIPTION = c("Big", "Small", "Medium", "Very Big"),
                stringsAsFactors = FALSE)

Answer 2

要一次性合并多个数据框，EXEC master.dbo.sp_MSset_oledb_prop N'Microsoft.ACE.OLEDB.12.0' , N'AllowInProcess', 1 GO EXEC master.dbo.sp_MSset_oledb_prop N'Microsoft.ACE.OLEDB.12.0' , N'DynamicParameters', 1 GO通常很有帮助：

Reduce

如您所见，所有数据框中存在的列都添加了后缀（默认为out <- Reduce(function(x,y) merge(x,y, by = "CLASS", all.x=T), list(df1, A, B)) out CLASS ID DESCRIPTION.x DESCRIPTION.y 1 1 A Unknown Big 2 1 B Unknown Big 3 1 A Unknown Big 4 2 A Tall Small 5 4 B <NA> Very Big行为）。这使您可以应用任何逻辑，以获得所需的最后一列。例如，

merge

请注意，out$Description <- ifelse(out$ID == "A", as.character(out$DESCRIPTION.x), as.character(out$DESCRIPTION.y)) > out CLASS ID DESCRIPTION.x DESCRIPTION.y Description 1 1 A Unknown Big Unknown 2 1 B Unknown Big Big 3 1 A Unknown Big Unknown 4 2 A Tall Small Tall 5 4 B <NA> Very Big Very Big是矢量化的并且非常有效。

Answer 3

一种dplyr解决方案：

library(dplyr)
bind_rows(lst(A,B),.id="ID") %>% inner_join(df1)
#   ID CLASS DESCRIPTION
# 1  A     1     Unknown
# 2  A     1     Unknown
# 3  A     2        Tall
# 4  B     1         Big
# 5  B     4    Very Big

根据列值合并不同的数据帧

3 个答案: