Expressions - Returning a number when using a length

leecasey · April 2023

Hi I'm having a bit of trouble generating an integer for a pattern number from an expression which is using an length (mm).

floor((#length/2)/60)

I'm assuming the issue is incompatible types but not sure how to solve it. Is there any way to cast #length as an int?

S1mon · April 2023

You can divide by 1 mm to get rid of the units, but I'm a little unclear how you're trying to use this calculation.

I didn't test this, but something like this should work:
floor((#length/2)/60)/(1 mm)

If you ever change the units of the document it's going to break, and I can't quickly think of a way to make this so that it will just get rid of the units in a universal way.

_anton · April 2023

Simon is correct. FWIW, though, I'd flip the logic around: make a variable like #number_of_instances, then make a #length variable computed from that. That makes it easy to update things and saves you from having to floor() anything.

S1mon · April 2023

You might also want to look at Linear Pattern Plus. It might solve your needs without needing to write any expressions.

https://forum.onshape.com/discussion/18076/new-feature-linear-pattern-plus/p1

leecasey · April 2023

Unfortunately that didn't work. Here's a better explanation of what I'm trying to achieve. I need to pattern some holes on this rail, the pattern must be central to the rail, hence why I'm dividing the length by 2. So I just want to generate the number of holes in the pattern from the length in mm.

Image: https://us.v-cdn.net/5022071/uploads/editor/ly/6q3xagw9nop0.png

leecasey · April 2023

Thank you, the above didnt work but a little change of parenthesis did the job!

floor(#length/2/60/(1mm))

NeilCooke · April 2023

You also don’t need the “1” - just “mm” will do.

EvanReese · April 2023

This is exactly the kind of situation I wrote Linear Pattern Plus for (as Simon mentioned). in your case, is the 60 the hole spacing? if so, you could also just make it 60mm and that'd do it. length/length = number

leecasey · April 2023

Thanks everyone. 👍 will certainly check out LPP, Evan. 🙂

vanowm · April 29

https://forum.onshape.com/discussion/comment/91300#Comment_91300

Can someone please explain this nonsense? dividing length by a number = length, dividing length by a length = number? WTF?

EvanReese · April 29

Think of units as something that can be divided out. mm/mm = 1 and in/mm = 25.4

Since #length has units in it already, to get a number for the floor function, you have to divide by units. So if #length = 5mm you could get just 5 with #length/mm = 5

_anton · April 29

https://forum.onshape.com/discussion/comment/116552#Comment_116552

How do you divide a meter in half? 1m / 2, which is a length. How many 50cm lengths are in a meter? 1m / (50cm), which is a number.

vanowm · May 3

https://forum.onshape.com/discussion/comment/116598#Comment_116598

That is actually a brilliant explanation. Thank you!

Expressions - Returning a number when using a length

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