r programming --- merge function returns column names with .x and .y -

while merging 2 tables, can't control column names in merge result. explain situation, let me use mtcars data:

#load mtcars data.frame data(mtcars) 

add new column called 'car' use merging key

mtcars$car <- row.names(mtcars) 

now create 2 mutually exclusive tables.

small <- mtcars[mtcars$cyl == 4,] med.large <- mtcars[mtcars$cyl >4,] 

now when left merge, should 'small' table 2 tables mutually exclusive:

merge(x = small, y = med.large, = 'car', all.x=t) 

this returns 'small' table every column appears twice .x , .y extension .y columns na (since 2 tables have no common records) , looks following

 car mpg.x cyl.x disp.x hp.x drat.x  wt.x qsec.x vs.x am.x gear.x carb.x mpg.y cyl.y   1      datsun 710  22.8     4  108.0   93   3.85 2.320  18.61    1    1       4      1    na    na 

how can column names once column values primary merge table in case left table ('small'). don't know how avoid .x , .y. extension?

if every column name repeated, can use

merge(x = small, y = med.large, = names(small), all.x=t) 

if column names differ, can build vector of names in both with

intersect(names(small), names(med.large)) 

and pass by. otherwise, if 2 data.frames share column not passed by, you'll end .x or .y type subscripts.