Avoiding and renaming .x and .y columns when merging or joining in r

Question

Often I go about joining two dataframes together that have the same name. Is there a way to do this within the join-step so that I don't end up with ax and ay column? So the names might be 'original_mpg', and 'new_mpg'?

  library(dplyr)
  left_join(mtcars, mtcars[,c("mpg",'cyl')], by=c("cyl"))
  names(mtcars) #ugh

Answer 1

Currently, this is an open issue with dplyr . You'll either have to rename before or after the join or use merge from base R, which takes a suffixes argument.

Answer 2

The default suffixes, c(".x", ".y") , can be overridden by passing them as a character vector of length 2:

library(dplyr)    
left_join(mtcars, mtcars[,c("mpg","cyl")], 
              by = c("cyl"), 
              suffix = c("_original", "_new")) %>% 
      head()

Output

 mpg_original cyl disp  hp drat   wt  qsec vs am gear carb mpg_new
1           21   6  160 110  3.9 2.62 16.46  0  1    4    4    21.0
2           21   6  160 110  3.9 2.62 16.46  0  1    4    4    21.0
3           21   6  160 110  3.9 2.62 16.46  0  1    4    4    21.4
4           21   6  160 110  3.9 2.62 16.46  0  1    4    4    18.1
5           21   6  160 110  3.9 2.62 16.46  0  1    4    4    19.2
6           21   6  160 110  3.9 2.62 16.46  0  1    4    4    17.8

Answer 3

You can use suffix with a slightly modified function I found in the help of strsplit to make it a prefix

library(dplyr)    
mt_cars <- left_join(mtcars, mtcars[,c("mpg","cyl")], 
              by = c("cyl"), 
              suffix = c("_original", "_new"))
strReverse <- function(x){
   sapply(lapply(strsplit(x, "_"), rev), paste, collapse = "_")
}
colnames(mt_cars) <- strReverse(colnames(mt_cars))

Answer 4

Well, I had a similar question when I found this post. I found a different solution to the question that I hope helps.

The solution is actually fairly simple, you generate a list with all the data frames you want to merge and use the reduce function.

library(dplyr)   

df_list <- list(df1, df2, df3)
df <- Reduce(function(x, y) merge(x, y, all=TRUE), df_list)

This was a solution to another problem I had, I wanted to simplify merging multiple dataframes. But if you use two dataframes in the list, it works all the same and merging does not rename the columns.