Alex van den Bogaerdt wrote: > > However, when I'm displaying the graph for the current month, the >> PERCENT function is using all the unknown future values in the >> calculation > >sure > >> causing it to be incorrect. > >Why?
Seems obvious enough to me ! >You seem to know about your "unknown" data. That means it isn't >as unknown as the name suggests... Just because you know that it's unknown doesn't make it any less unknown in value - without wanting to sound like a politician talking crap about unknown unknowns and known unknowns ! > > As a very simplified example, say I'm 10 days into a month (with 20 days >> remaining) and the values so far look like this: >> >> 1,2,3,4,5,6,7,8,9,10 >> >> The 90th percentile should be 9 > >according to what/who ? Common usage ? Seems obvious enough to me that 9 is the value which 90% of the values in the list are equal or less than. Isn't that what a percentile is about. OK, it's a bit coarse with so few samples. > > I have looked through the documentation and can't find any mechanism >> which would allow me to restrict the PERCENT function to a specific date >> range (to exclude values in the future), or exclude NaN values. > >Why graph values in the future, you know this won't include useful data. But it may well produce useful graphs ! For some reason accountants seem to like pigeonholing numbers into arbitrary calender units unrelated to what's actually going on in a business. One example that comes easily to mind is an accountant who wants the sales figure for the current month graphing - not the last 30 days, but the current calendar month. Unless you have found a working crystal ball, at any point before the end of the month you will unknown values in the graph. If the above samples (ie 1 .. 10) were values for the 1st through 10th of the month, then the right place to draw the line would be at 9 - ignoring unknown values for 11 through 28,30,31. If you assumed zero for future samples then the line would incorrectly end up at 7. Similarly your average would end up at a little under 2 instead of 5.5 ! I don't think any accountant would accept 2.2 as an average of sales so far this month from those numbers. Changing things a little, suppose there are 10 units of sales on day 1, would you accept a figure of .33 units/day as the average sales so far this month or would you expect 10 ? As another example, my ISP will give me graphs of my bandwidth usage over a billing period. On 10th of each month it starts out with a nearly empty graph and it fills up until the 9th of the following month. What's useful for me is not an average calculated as "total to date/30" but total to "date/day so far". OK, it would probably be equally (possibly more) useful to show "last 30 days", but current billing period is what we get. >try changing unknown into some known value, like zero or a very large >negative number I fail to see how that will help - it will just further skew the data. The answer would appear to be to do the calculations over the range "1st of month" to "today" whilst plotting them on an X axis from "1st of month" to "end of month" - is that easy to do ? -- Unsubscribe mailto:[EMAIL PROTECTED] Help mailto:[EMAIL PROTECTED] Archive http://lists.ee.ethz.ch/rrd-users WebAdmin http://lists.ee.ethz.ch/lsg2.cgi