what is the optimized way to combine multiple dataframes into one dataframe ?

[Devi P.V]

Hi all,

I have 4 data frames with three columns,

client_id,product_id,interest

I want to combine these 4 dataframes into one dataframe.I used union like
following

df1.union(df2).union(df3).union(df4)

But it is time consuming for bigdata.what is the optimized way for doing
this using spark 2.0 & scala


Thanks