Left join only selected columns in R with the merge() function

I think it's a little simpler to use the dplyr functions select and left_join ; at least it's easier for me to understand. The join function from dplyr are made to mimic sql arguments.

 library(tidyverse)

 DF2 <- DF2 %>%
   select(client, LO)

 joined_data <- left_join(DF1, DF2, by = "Client")

You don't actually need to use the "by" argument in this case because the columns have the same name.

Alternative solution using left_join() and select() from the dplyr package, without intermediate steps:

DF1 <- DF1 %>%
  left_join(DF2, by = "Client") %>%
  select(-CON)

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 :)

Nothing elegant but this could be another satisfactory answer.

merge(x = DF1, y = DF2, by = "Client", all.x=TRUE)[,c("Client","LO","CON")]

This will be useful especially when you don't need the keys that were used to join the tables in your results.