match/merge dataframes with a number columns with different column names in r

Question

I have two dataframe with different columns that has large number of rows (about 2 million)

The first one is df1

The second one is df2

I need to get match the values in y column from table one to R column in table two Example: see the two rows in df1 in red box have matched the two rows in df2 in red box

Then I need to get the score of the matched values

so the result should look like this and it should be stores in a dataframe:

My attempt : first Im beginner in R, so when I searched I found that I can use Match function, merge function but I did not get the result that I want it might because I did not know how to use them correctly, therefore, I need step by step very simple solution

Answer 1

 merge(df1,df2,by.x="y",by.y="R")[c("y","score")]
    y score
1   2     3
2 111     4

Answer 2

We can use match from base R

df2[match(df2$R, df1$y, nomatch = 0), c("R", "score")]
#   R score
#3   2     3
#4 111     4

---

Or another option is semi_join from dplyr

library(dplyr)
semi_join(df2[-1], df1, by = c(R = "y"))
#    R score
#1   2     3
#2 111     4