当重复加入变量时存在内连接

Question

  

可能重复：
  How to join data frames in R (inner, outer, left, right)?

This question很好地介绍了R中的联接。

内连接上的Wikipedia article非常有用。

我想在基础R中重现这个结果。我不认为以下工作：

merge(employee,department,all=T)
merge(employee,department)

因为合并变量有重复。

但是，sqldf有效：

library(sqldf)
sqldf("select * from employee  inner join department ON employee.DepartmentID = department.DepartmentID")

我的问题是：

1. 这是否意味着合并不会在此处执行内部联接。

2. 如何在基础R中完成此连接。

以下是两个可以从网站和上面的例子中使用的数据框架。

employee <- structure(list(LastName = c("Rafferty ", "Jones", "Steinberg", 
"Robinson", "Smith", "John"), DepartmentID = c("31", "33", "33", 
"34", " 34", " .")), .Names = c("LastName", "DepartmentID"), class = "data.frame", row.names = c(NA, -6L))

department <- structure(list(DepartmentID = c(31L, 33L, 34L, 35L), DepartmentName =    structure(c(4L,2L, 1L, 3L), .Label = c("Clerical", "Engineering", "Marketing", "Sales"), class = "factor")), .Names = c("DepartmentID", "DepartmentName"), class = "data.frame", row.names = c(NA, -4L))

Answer 1

Julieth，

请查看这是否适合您。我检查了数据结构的结构，看看为什么结果不符合预期。

str(department)
str(employee)
employee$DepartmentID <- as.numeric(employee$DepartmentID)
merge(employee,department)