By using the merge function and its optional parameters:
Inner join: merge(df1, df2) will work for these examples because R automatically joins the frames by common variable names, but you would most likely want to specify merge(df1, df2, by = "CustomerId") to make sure that you were matching on only the fields you desired. You can also use the by.x and by.y parameters if the matching variables have different names in the different data frames.
Outer join: merge(x = df1, y = df2, by = "CustomerId", all = TRUE)
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 "CustomerId" to R as the matching variable. I think it's almost always best to explicitly state the identifiers on which you want to merge; it's safer if the input data.frames change unexpectedly and easier to read later on.
You can merge on multiple columns by giving by a vector, e.g., by = c("CustomerId", "OrderId").
If the column names to merge on are not the same, you can specify, e.g., by.x = "CustomerId_in_df1", by.y = "CustomerId_in_df2" where CustomerId_in_df1 is the name of the column in the first data frame and CustomerId_in_df2 is the name of the column in the second data frame. (These can also be vectors if you need to merge on multiple columns.)
You can do this by subsetting the data you pass into your merge:
merge(x = DF1, y = DF2[ , c("Client", "LO")], by = "Client", all.x=TRUE)
Or you can simply delete the column after your current merge :)
Best Answer
This may be because the values in column1 from df2 are not a 1-1 mapping. Meaning a single value in column1 may be related to more than one value in column2. You can check this by using
table(df2$column1). If you find a value from column1 with a count > 1 then this is the reason.Also I would like to recommend an alternative if you are more comfortable with sql there is a very nice library called
sqldfwhich allows you to use sql like queries on your data frames!