add specific fields in for loop

Hi Team,
I can write a for loop like this:
for (i in columns(df)){
? ......
}

But it will working on all column in dataframe df. If I want to work on some of specific fields (say: the fields' name content 'date'), how should I modify the for loop? I changed the code below, but it doesn't work.
for (i in columns(df) %in% 'date' ){
? .....
}


Thank you,
Kai