Summing based on multiple attribute filtering

Dear OFT,

I had to calculate a sum using an attribute from a child table and apply it to the parent table. Stefano Ricci suggested the following expression sum(spl.stand[species == '1'].treevolume). This approach started working as intended, summing values based on the filtered species where the code is 1. Now, I am aiming to perform a similar sum operation using multiple attribute filters. it will help me greatly to reduce creating extra fields(attribute). I've tried a script like this: sum(spl.stand[species == '1'][starta == 'tree'].treevolume). However, this script exhibits the same behavior as before. It neither displays any incorrect syntax nor generates any output; instead, it hangs indefinitely, preventing me from progressing to the next page. I am unsure whether my script sum(spl.stand[species == '1'][starta == 'tree'].treevolume) is in an incorrect format or if it's not permissible to filter based on multiple attributes, or if there's another issue altogether. I would greatly appreciate your expert suggestions to resolve this matter. Thank you in advance. -Rajkumar Rimal