r - Reorder few columns only out of hundreds -

what efficient way reorder columns data frames hundreds thousands of columns?

the following tried , works, looking optimal function.

dput(names(df1)) dump column names , used in following step

swapped columns df1[c(col1, col3, col2,.....col99,col100)

ex names(df1) "col1" "col2" "col3".............."col99" "col100" 

want swap "col2" , "col3",

names(df1) "col1" "col3" "col2".............."col99" "col100" 

df1 = df1[,c(1,3,2,4:100)] 

reorders columns according permutation c(1,3,2,4:100)