new: materialize, to turn virtual columns into real ones (not 100% convinced of this API)
new: materialize, to turn virtual columns into real ones (not 100% convinced of this API)

maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex