 # Nested loop controlled by external slider in python grasshopper

hello,
I am trying to create a nested tree loop between months , days and hours controlled by an outer slider, that can control the nested tree loop (in python grasshopper) as an example:
month m: 1,2,3
day d: 1 2 3
hours h: 10, 13, 16
external slider from zero to 27

the expected outcome for this tree nested loop is:

when the external slider is zero
the output is : [1,1,10]

when the slider is 1
the output is :[1,1,13]

when the slider is 2
the output is:[1,1,16]

when the slider is 3
the output is : [1,2,10]

when the slider is 4
the output is:[1,2,13]
ect…
so how could I reach this part??
any help?
thank you
Best regards
Fatima.b

Hi Fatima, How is this?

``````months = [1,2,3]
days = [1,2,3]
hours = [10,13,16]
def output(n): return [months[n//9], days[(n%9)//3], hours[n%3]]
``````

best regards,
Graham

Dear Graham,
I will try it
Best Regards
Fatima B

Dear Grahm,
I have try it but it did not give me the result that I have mention it in my previous question. the result is now null
the result that i want is
[1,1,10]
[1,1,13]
[1,1,16]
[1,2,10]
[1,2,13]
[1,2,16]
[1,3,10]
…[3,3,16]
Kindly check the file below
and what do you mean by n . n is what ?
nested loop controled by u.gh (7.0 KB)
thank you
best regards

Hello Fatima,
n is your slider value - I see you have used u for this
Using the file you sent I have simply replaced the Python script block with `b = [x[u//9], y[(u%9)//3], z[u%3]]`
This seems to work with the exception of value 27 : you only need inputs from 0 to 26 Dear Graham,
Thank you sooo much it is working
best regards
fatima.b

1 Like

Dear Graham,
If I want to add another parameter for example
in addition to the hours,days and months I ant to add angle (which are(0,30,60,90))
so we have 4 different parameters
so the output that i wanted is
[1,1,10,0]
[1,1,10,30]
[1,1,10,60]
[1,1,10,90]
[1,1,13,0]
[1,1,13,30]
[1,1,13,60]
[1,1,13,90]

so I should add to the formula which wasb = [x[u//9], y[(u%9)//3], z[u%3]]
since I have an additional parametrs that is the angles
Best regards
Fatima b

Hello,
yes you need to add a 4th input `d = [0,30,60,90]`
to calculate the list indices you could use

``````ix = u//36
iy = (u//12)%3
iz = (u%12)//4
id = u%4
b = [x[ix], y[iy], z[iz], d[id]]
``````

This is all using modular arithmatic to calculate the list indices.

Dear Graham
Thank you again and again
now it is working
but I need to understand these formula for example why % and why we use // ? there is any way that can help me to understand it?

Best regards
Fatima B

You’re very welcome Modular arithmetic is really useful for this type of thing so it is worth working on it, especially if you need to work with large data sets. I would start by writing out the full list and thinking about where you need to start counting from (using %) and what step size you need to take (using //)
It is a little opaque though!!! A slower but clearer solution would be using nested loops to build a list of all possible answers and then just outputting the one you need:

``````outputs = []
for month in x:
for day in y:
for hour in z:
for angle in d:
outputs.append([month,day,hour,angle])
b = outputs[u]
``````