Left join only selected columns in R with the merge function

Question

I am trying to LEFT Join 2 data frames but I do not want join all the variables from the second data set   As an example  I have dataset 1  DF1      Cl    Q   Sales  Date    A    2   30     01 01 2014    A    3   24     02 01 2014    A    1   10     03 01 2014    B    4   10     01 01 2014    B    1   20     02 01 2014    B    3   30     03 01 2014   And I would like to left join dataset 2  DF2    Client  LO  CON    A    12  CA    B    11  US    C    12  UK    D    10  CA    E    15  AUS    F    91  DD   I am able to left join with the following code   merge x   DF1  y   DF2  by    Client   all x TRUE        Client Q    Sales   Date             LO      CON    A      2    30      01 01 2014       12      CA    A      3    24      02 01 2014       12      CA    A      1    10      03 01 2014       12      CA    B      4    10      01 01 2014       11      US    B      1    20      02 01 2014       11      US    B      3    30      03 01 2014       11      US   However  it merges both column LO and CON  I would only like to merge the column LO      Client Q    Sales   Date             LO          A      2    30      01 01 2014       12          A      3    24      02 01 2014       12          A      1    10      03 01 2014       12          B      4    10      01 01 2014       11          B      1    20      02 01 2014       11         B      3    30      03 01 2014       11

User · Answer

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.

User · Answer

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  lt - DF2   gt      select client  LO    joined data  lt - 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

User · Answer

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

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

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