R: find date closest to row specific date : I have the following dataframe in R
https://i.stack.imgur.com/buNOS.png



1st column contains identification numbers (respnr)
2nd column contains reference date per identification number (cdatalg)
3rd through 16th column contains dates (datesc1:datesc14)

I wish to enter a 17th column in which the date in column 3:16 is printed which is closest to the reference date in column 2. 
I have tried combinations of apply and which.min and neardate, though can't figure it out.

A push in the right direction would be very much appreciated. 