improve melt by keeping factors

4 jobs for master in 5 minutes and 31 seconds
latest
Status Name Job ID Coverage
  Test
passed package #2961
r-base-biosp

00:00:47

passed package-devel #2962
r-devel-biosp

00:00:48

passed package-mac #2964
Mac R

00:03:16

passed package-windows #2963
win10 R binaries

00:05:30