Calculate difference between two measurements

misipino · April 17, 2019, 9:33pm

Hi,
i would to graph the difference between A and B series in Grafana.

It’s possible?

This is my current chart:
https://snapshot.raintank.io/dashboard/snapshot/ZYNc6iJx7uwuX4nRSMwPbnQnjPYhJsps

clanlaw · April 18, 2019, 8:04am

I don’t know about other data sources, but if you are using influx you can use the query
`SELECT mean(“A”)-mean(“B”) FROM “whatever” WHERE $timeFilter GROUP BY time($interval) fill(none)

misipino · April 18, 2019, 10:01am

Use influx.The problem is that the difference should be made between two different measures.

How should the FROM be used?

Thanks

clanlaw · April 18, 2019, 12:37pm

I don’t think it is possible across measurements. You would have to put both variables in the same measurement.

github.com/influxdata/influxdb

Mathematics across measurements

opened 07:02PM - 04 Aug 15 UTC

srfraser

kind/feature-request area/influxql flux/triaged 1.x

Apologies if this is a duplicate, I had a look and couldn't see a relevant issue…. I can see from the documentation how to select from multiple measurements (although it calls them series, still, at https://influxdb.com/docs/v0.9/query_language/data_exploration.html ) For example, with data inserted by telegraf, you can do: `select * from disk_used,disk_total where host = 'myhostname' and path = '/'` How would you express that as a percentage? I've tried variations of the following, and none seem to work: `select disk_used.value/disk_total.value from disk_used, disk_total where host = 'myhostname' and path='/'` The "mydb"."retentionpolicy"."measurement" syntax doesn't work there, either. Is it a good idea to add aggregation functions for cases like `diff(value1, value2) from m1, m2` and `divide(value, value) from m1, m2`, or should the arithmetic operators be working? Also, I noticed when experimenting that it's also not possible to divide one derivative by another. For example, if I have two counters, bytes transferred and api calls made - both of which are constantly going up - how would you calculate the mean bytes per api call?

svetb · April 18, 2019, 1:01pm

I haven’t tried this myself, but in theory it’s possible these days with Flux; see https://www.influxdata.com/blog/influxdb-how-to-do-joins-math-across-measurements/
(Flux querying is available via a Grafana plugin)

kabeerandrabi · May 4, 2020, 12:49pm

Hi,
I’m facing a similar issue, i need to compare 2 times, of different versions, say R1 and R2, and plot the percentage difference in a 3rd column. How can it be done?
Thanks!

aleksas · June 15, 2021, 9:10am

After selecting measurmenets A and B, switch panel from Query to Transform. If none were selected find and select “Field From Calculation”. You’ll see your measurements, you can select Calculation: Difference to plot A-B

johnsturgeon · May 23, 2022, 4:38pm

This is the answer ^^^