Using the index of an array in calculations

Hi all, I’m starting out with Grasshopper, and would appreciate some learning assistance. I want a parametrised array of beams. The beams are all the same length, except the beams on the left and right edges of the array should be longer by a defined overhang. I solved this problem by checking when the start point X component was the same as the origin X component, and then subtracting the overhang, while on the right side checking for the end point being the same X dimension as the calculated number of beams times the span lengths. To me, this is a bit ugly, I would prefer to have used the array indices to check for the beam location and conditionally add the overhangs that way. However, I cannot find how to do this using the tree data structure. I’ve been through all the relevant video tutorials that I can find. Any suggestions?

Array of beams.gh (23.7 KB)

I’m not so clear on what it is you are trying to achieve, but here are a couple of different options that might work for you.

Array of beams_V2.gh (12.8 KB)

Thanks Adam, and sorry for the slow response. It was my first posting so the notification of your reply went to junk mail…

It’s not exactly what I was trying to achieve but the method you have used of reversing the list and looking at the zero elements is better, I will rework mine to use this.

I was wondering if there is a method for the more general case of selecting the nth item to alter, where n is a parameter?

Sets | List | List Item and Replace Items