How to merge data frames using joins

Question

Below are two data frames:

data1 = data.frame(Cust_Id = c(1:6), Product = c(rep("Headphones", 3), rep("Toaster", 3)))
data2 = data.frame(Cust_Id = c(2, 4, 6), State = c(rep("New York", 2), rep("California", 1)))

data1
#  Cust_Id   Product
#           1 Headphones
#           2 Headphones
#           3 Headphones
#           4   Toaster
#           5   Toaster
#           6   Toaster

data2
#  Cust_Id   State
#           2 New York
#           4 New York
#           6 California

How can I apply joins on these data frames?

• An inner join of data1 and data2:
  This returns only those rows in which the left table has matching keys in the right table.
• An outer join of data1 and data2:
  This should return all rows from both tables, basically joins records from the left which have matching keys in the right table.
• A left outer join or a simple left join of data1 and data2:
  This should return all rows from the left table, and any rows with matching keys from the right table.
• A right outer join of data1 and data2:
  This should return all rows from the right table, and any rows with matching keys from the left table.

Answer 1

You can use the merge function with it's optional parameters

Inner join: merge(data1, data2) will work .

This is because R  joins the frames by common variable names.

To make sure that you are matching by only those fields that you desire, you can specify the 'by' parameter like this:

 merge(df1, df2, by = "Cust_Id")

You can also use the by.x and by.y parameters if the matching variables have different names and are present in different data frames.

For all other joins you can use the commands mentioned below:

Outer join: merge(x = data1, y = data2, by = "Cust_Id", all = TRUE)

Left outer: merge(x = data1, y = data2, by = "Cust_Id", all.x = TRUE)

Right outer: merge(x = data1, y = data2, by = "Cust_Id", all.y = TRUE)

Cross join: merge(x = data1, y = data2, by = NULL)