---
title: "Other expression can not be combined with taxonProp function"
url: "https://openforis.support/questions/3476/other-expression-can-not-be-combined-with-taxonprop-function"
tags: ["arena", "collect"]
status: "answered"
score: 0
answer_count: 1
asked: "2022-10-31T07:40:21"
last_activity: "2022-11-08T23:19:13"
source: "Open Foris Support - Q&A Forum"
license: "Copyright Open Foris, 2026. Some rights reserved under creative commons license."
---

# Other expression can not be combined with taxonProp function

Asked by Rajkumar on 2022-10-31

Math.pow(2.71828182845905, a + b * Math.log(dbh) + c * Math.log(height_m)) / 1000

In this expression a, b and c are the extra properties of taxonomy. the value which had to take part with other expression. But it could not calculate the right value. Sometimes it calculates as blank cell, sometime 1 and sometime 0.01. It works fine if we put only taxonProp('trees','a',species) without messing other calculation. So, I created another attribute and put the right value using taxonProp('trees','a',species). Once the right value populated in the column it could be possible to produce the right value. I know, it is not a clever idea to do the work this way however it is working. In short, please, try to implement this type of expression like taxonProp('trees','a',species) X dbh or taxonProp('trees','a',species) X 10. (Here X is multiplication sign) Thank you very much. I am seriously waiting for the Arena update.


## Answer (score 0, by Stefano (OF) on 2022-11-08)

Link: https://openforis.support/questions/3476/other-expression-can-not-be-combined-with-taxonprop-function/3481

Dear Rajkumar,  
With the latest version of Arena you will be able to edit the Extra Properties of the taxonomy (in the taxonomy editor, using the top right gear button and selecting "Edit Extra Properties") and you can set the data type of your properties to "Number". Then your expression should work as expected.  
Many thanks,  
Open Foris Team