Dew Point Calculation

[adrianrepublic]

I am trying to produce or calculate the Dew Point in Celsius of data in two separate indexes.

I believe the offcial Dew point formula is Td = T - ((100 - RH)/5.)

I want to basically use this formula to produce Dew point using relative humidity on one index with temperature on another index

[to4kawa · Accepted solution]

Assuming that the measurement times at the two indexes are the same,

index=relative_humidity_index OR index=temperature_index
|stats avg(relative_humidity) as relative_humidity avg(temperature) as temperature by _time
|eval dew_point=temprature-((100-relative_humidity)/5.0)

[adrianrepublic]

That nearly worked. Thanks 🙂

(index="index1" device=* customer_id=*) OR (index="weather") | stats avg(hum) as relative_humidity avg(temp) as temperature by customer_id | eval dew_point=temperature-((100-relative_humidity)/5.0)

However something which ive noticed which could be any issue is that the both indexes have a temperature but on one index its temperature(weather index) and on the other its temp(index 1). When i change it to temperature it doesnt seem to produce/include the values from the "weather" index.

I basically want the temperature from the weather index vs humidity of the index1

[richgalloway]

Easily handled.

(index="index1" device= customer_id=) OR (index="weather") 
| eval temperature=coalesce(temperature, temp)
| stats avg(hum) as relative_humidity avg(temp) as temperature by customer_id 
| eval dew_point=temperature-((100-relative_humidity)/5.0)

[adrianrepublic]

richgalloway that seems to have done the job 🙂 Thanks very much.