[R] Duplicate of columns when merging two data frames

[MacQueen, Don]

You have duplicates after merging because, although you know they are the
same, the R merge() function does not. And the people who wrote that
function knew that sometimes two columns with the same name are not
identical.

Since you know that the columns are identical, drop the column from one of
the two data frames before merging.

-Don

-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 3/13/14 8:19 AM, "Stefano Sofia" <stefano.sofia at regione.marche.it>
wrote:

>Dear list users,
>I have two data frames df1 and df2, where the columns of df1 are
>
>Sensor_RM Place_RM Station_RM Y_init_RM M_init_RM D_init_RM Y_fin_RM
>M_fin_RM D_fin_RM
>
>and the columns of df2 are
>
>Sensor_RM Station_RM Place_RM Province_RM Region_RM Net_init_RM
>GaussBoaga_EST_RM GaussBoaga_NORD_RM Gradi_Long_RM Primi_Long_RM
>Secondi_Long_RM Gradi_Lat_RM Primi_Lat_RM Secondi_Lat_RM Long_Cent_RM
>Lat_Cent_RM Height_RM
>
>When I merge the two data frames through
>
>df3 <- merge(df1, df2, by=c("Sensor_RM", "Station_RM"))
>
>I get a new data frame with columns
>
>Sensor_RM Station_RM Place_RM.x Y_init_RM M_init_RM D_init_RM Y_fin_RM
>M_fin_RM D_fin_RM Place_RM.y Province_RM Region_RM Net_init_RM
>GaussBoaga_EST_RM GaussBoaga_NORD_RM Gradi_Long_RM Primi_Long_RM
>Secondi_Long_RM Gradi_Lat_RM Primi_Lat_RM Secondi_Lat_RM Long_Cent_RM
>Lat_Cent_RM Height_RM
>
>I am sure that df1$Place_RM and df2$Place_RM are equal. I checked it from
>the shell using awk and diff.
>Why then I have a duplicate of Place_RM, i.e. Place_RM.x and Place_RM.y,
>and only of them?
>
>Thank you for your help
>Stefano
>
>
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