How to join merge data frames inner outer left right

Question

Given the following two data frames:

data.frame = df1

(c(1:6), Product = c(rep("Toaster," 3), rep("Radio," 3))
data.frame = df2
State = c(rep("Alabama", 2), rep("Ohio", 1)) (CustomerId = c(2, 4, 6), State = c(rep("Alabama", 2), rep("Ohio", 1))

Product # 1 Toaster # 2 Toaster # 3 Toaster # 4 Radio # 5 Radio # 6 Radio df1 # CustomerId df1 # CustomerId df1 # CustomerId df1 # CustomerId df1 # CustomerId df1 #

# CustomerId State # 2 df2 # CustomerId Alabama is ranked fourth. Alabama is ranked sixth. Ohio
How do I perform database-style joins, i.e. sql-style joins?

Answer 1

The merge function and its optional parameters allow you to:

R automatically joins the frames by common variable names, thus the inner join merge(df1, df2) will work for these cases. However, you should probably specify merge(df1, df2, by = "CustomerId") to ensure that you were matching on exactly the fields you required. If the matching variables have different names in the various data frames, you may also use the by.x and by.y arguments.

Merge: outer join

(by = "CustomerId," all = TRUE, x = df1, y = df2)

Left outer: merge(x = df1, y = df2, by = "CustomerId", all.

x = TRUE)

Right outer: merge(x = df1, y = df2, by = "CustomerId", all.

y = TRUE)

Cross join: merge

(x = df1, y = df2, by = NULL)

Just as with the inner join, you would probably want to explicitly pass