# LOD expression

**Kirandeep Singh**Feb 1, 2019 2:40 AM

Greetings to fellow tableau users, I am new to tableau desktop and tableau in general. I am currently completing my accounting degree course in Malaysia. The reason i am writing this forum is because i am having a tough time understanding **LOD expression and applying it in real case scenario. **I understand the basic concept of ** Include, Exclude and Fixed** but i don't understand what is the purpose of the mentioned types of** LOD expression in dept**. It would be great if someone can explain with clarity, as it will be really helpful to apply in challenging cases.

However i do have a question which i need help resolving, the question is** " A single order can include multiple items across multiple product categories. Each item will be on a different row of the data, but the rows will share a single Order ID. Find the average sales value for orders which include office supplies". **My trouble for this question is finding the Average sales for a specific category **( Office Supplies) using LOD expression. **I have tried using Fixed LOD formula **SUM({Fixed[Order ID]:max(IF[Product Category]="Office Supplies"THEN 1 ELSE END)}*[SALES])/COUNTD(IF[Product Category]="Office Supplies" THEN[OrderID] ELSE NULL END).** However the calculation is errored and i can't find other ways either using LOD expression.

My second question is pertaining this question " **How many days in January of 2011 had a positive total profit" **this is my last question and the main focus is** specific to month of january and and positive profit for the year 2011,** which i am struggling to apply. I know it is using Fixed LOD but not sure how to condition it.

I have attached my** workbook package below together with the sample data**. I hope to learn more via this platform to enhance my tableau skills and at same time be useful in future to help others.