I have two columns of data, production in tons and emissions in lbs for each
calendar day, no missing data, but can have values=0 (no production).
What I what to do is calculate a 30-day rolling average of emission
lbs/production tons using the last 30 production values that are greater than
zero.
For simplicity, in example below, assume I am looking for a 5-day rolling
average
A B C D
Date Production Emissions 5-day average
(tons) (lbs) (lb/ton)
1/1/09 10,000 2,000 n/a
1/2/09 5,000 1,000 n/a
1/3/09 5,000 1,000 n/a
1/4/09 5,000 1,000 n/a
1/5/09 5,000 1,000 0.200 (=6,000 lbs/30,000 tons)
1/6/09 8,000 1,000 0.179 (=5,000 lbs/28,000 tons)
1/7/09 0 0 0.179 (=5,000
lbs/28,000 tons)
1/8/09 0 0 0.179 (=5,000
lbs/28,000 tons)
1/8/09 9,000 3,000 0.219 (=7,000 lbs/32,000 tons)

Thanks in advance!