InfoPath Dev

I am pretty new to info path. I inherited a form and I need to make some enhancements. I have a drop down that pulls values from a SharePoint list. I would like to take the value the user chooses and then compare it to another list in SharePoint. After this is done I would like another field to be set based on what was chosen in the previous dropdown. I hope this makes sense. Thanks in advance.

Add a new data connection to your form that points to the 2nd sharepoint list you want to reference.  Pull in the fields that you need to compare or use to set the values of other fields in your form.  Then you need to set a rule on the dropdown that is connected to the 1st sharepoint list.  I am assuming that these lists have data that matches (i.e. a part number, or a username, etc.).  So then you would say for your rule "set a fields value".  In the first box, select the field from your infopath form that you would like to set.  Then in the next box, click the fx button.... Click insert field or group.  Choose the field that holds the value you want from sharepoint list2, then click filter..... in the first dropdown select the value from sharepoint list2 that should match the dropdown, in the second dropdown select "is equal to", in the third dropdown, select the current field (the dropdown field from your form).

That worked. Thank you. I was almost there except I didn't have the filter part.