How to Perform Left Join Using Selected Columns in dplyr

You can use the following basic syntax in dplyr to perform a left join on two data frames using only selected columns:

library(dplyr)

final_df <- df_A %>% 
  left_join(select(df_B, team, conference), by="team")

This particular example will perform a left join on the data frames called df_A and df_B, joining on the column called team, but only the team and conference columns from df_B will be included in the resulting data frame.

The following example shows how to use this syntax in practice.

Example: Perform Left Join Using Selected Columns in dplyr

Suppose we have the following two data frames in R:

#create first data frame
df_A <- data.frame(team=c('A', 'B', 'C', 'D', 'E'),
                   points=c(22, 25, 19, 14, 38))

df_A

  team points
1    A     22
2    B     25
3    C     19
4    D     14
5    E     38

#create second data frame
df_B <- data.frame(team=c('A', 'C', 'D', 'F', 'G'),
                   conference=c('W', 'W', 'E', 'E', 'E'),
                   rebounds=c(14, 8, 8, 6, 9),
                   assists=c(4, 3, 9, 9, 4))

df_B

  team conference rebounds assists
1    A          W       14       4
2    C          W        8       3
3    D          E        8       9
4    F          E        6       9
5    G          E        9       4

We can use the following syntax in dplyr to perform a left join but only bring in columns team and conference from df_B:

library(dplyr)

#perform left join but only bring in team and conference columns from df_B
final_df <- df_A %>% 
  left_join(select(df_B, team, conference), by="team")

#view final data frame
final_df

  team points conference
1    A     22          W
2    B     25         NA
3    C     19          W
4    D     14          E
5    E     38         NA

The resulting data frame contains all rows from df_A and only the rows in df_B where the team values matched.

By using the select() function from dplyr, we were able to specify that we only wanted to bring in the team and conference columns from df_B.

Notice that the rebounds and assists columns from df_B were not included in the final data frame.

Note: You can find the complete documentation for the left_join() function in dplyr here.