# Why do I need a Helper when I know the Item?

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Hi there,

Quantrix is logical und structured, and a cool thing. But there is one thing I do not understand, and I’m crossing the same thing in a lot of places, when doing SELECT statements, or in other places. I’m still not sure if my brain is twisted or if it is Quantrix ðŸ™‚

I compiled a very simple example to illustrate the point.

In a 3-dim matrix, I want to select one index on one dimension, sum over the second dimension, and do it for all elements in the third dimension.

Easy, as I know the item I want to slice – “S1” – by name.

I do not find a way to do this … not using the item name, not using the descriptor. Everybody is doing this using a helper. Why do I need to convert the address to content, and then search the cell content to get back the address of the cell?? This looks very inefficient to me.

Is there anybody out there who can fix my mind? Or show me how to solve the problem without a helper column (and yes, I know how I can do it if both matricies have the same structure and linked categories, I could sum over all “Sektor”-items, but that’s not what I want to do …

gilles Selected answer as best November 18, 2022

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Gilbert, try another formula version, plz:
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It looks like a Mac version of QM doesn’t recognize such formula syntax’s.
These two formulas are complete equivalents. The first one is just shorter.
1. The @Data::Sektor:(Years):(Linien) expression virtually propagates the item names of the Sektor category as many times as the Years and Linien categories have items: size(#Years) * size(#Linien) = 7 * 7 = 49 times in your case).
2. Function slice() is undocumented, it may be replaced by list() function. It assign only one Jahre category item name to the current cell rather then a list its names.
Also note, you can explicitly specify the literal (“S2“, for example) in the formula, this is that you requested in your post above.

Good luck

S A U Answered question November 17, 2022