Question

Possible Duplicate:
How to join data frames in R (inner, outer, left, right)?

This question nicely goes over joins in R.

And the Wikipedia article on inner join is useful.

I would like to reproduce this result in base R. I don’t think the following work:

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

because of the duplicates on the merging variable.

However, sqldf works:

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

My questions are:

1. Does this mean that merge does not perform an inner join here.

2. How can I accomplish this join in base R.

Here are two data.frames to work with from the website and example above.

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,

Please see if this works for you. I inspected the structure of the data structures to see why the results were not what was intended.

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