R Join Columns

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Rows in y with no match in x will have NA values in the new columns. If there are multiple matches between x and y, all combinations of the matches are returned. Fulljoin return all rows and all columns from both x and y. Where there are not matching values, returns NA for the one missing. Filtering joins keep cases from the left-hand data.frame: semijoin. # We can use the rbind function to stack data frames. Make sure the number of # columns match. Also, the names and classes of values being joined must match. # Here we stack the first, the second and then the first again: rbind(first, second, first).

If you want to use dplyr left join or any other type of join in R to combine information from two or multiple data frames, this post might be very helpful. Here is how to left join only selected columns in R.

The first data frame.

The second data frame.

Join

How to perform dplyr left join and keep only necessary columns from the second data frame? In this case, let’s keep only elephants and cats.

To do that, use the select function that defines what comes from the second data frame.

Here are two different ways of how to do that.

Columns

R Join On Two Columns

Here is another post that might be useful in your toolbox – multiple left joins in R.

If you browse through our technical blog posts you’ll see quite a few devoted to the data analysis functionality in the R packge dplyr. This is due to the fact that we are constantly finding fun new functions to play with. We wanted to devote this small post to an unexpectedly useful function called anti_join.

R Join Columns Must Be Present In Data

Two

Using anti_join() from the dplyr package

For most data analysis tasks you may have two tables you want to join based on a common ID. This is straightforward in any data analysis package. But occasionally, especially in quality assurance types of settings, we find ourselves wanting to identify the records from one table that did NOT match the other table. For example, anti_join came in handy for us in a setting where we were trying to re-create an old table from the source data. We then wanted to be able to identify the records from the original table that did not exist in our updated table. This is where anti_join comes in, especially when you’re dealing with a multi-column ID.

We’ll start with a relatively simple example.

To identify the rows that exist in table1 but not in table2 you could use any number of strategies:

You might ask why anti_join is an advance given the other easy solutions we’re showing above. We find it most useful when our common ID is a combination of multiple columns. So let’s use another example where we have a multi-column common ID:

R Join Columns Different Names

With a two-column unique ID using %in% or match() is more challenging. You could create a single ID by concatenating the state/county fields but this adds a messy extra step. Instead anti_join() is your savior: