I have a DF ID VALUE 100 120 101 100 102 100 103 104 105 .... when i calculate the sum of the values, it returned NA. should I populate the blank value as 0? Thanks, -- View this message in context: http://r.789695.n4.nabble.com/MISSING-VALUE-IN-R-tp2299586p2299586.html Sent from the R help mailing list archive at Nabble.com.