In that case, there are values >1, which is clearly not what I wanted. Thanks. I think I should use prop.table -- View this message in context: http://r.789695.n4.nabble.com/how-to-divide-each-column-in-a-matrix-by-its-colSums-tp3062739p3062752.html Sent from the R help mailing list archive at Nabble.com.