Parse Data tree branches into 2d array or their own array : python

I'm working with a simple data tree, in python.

the data tree is just two points on their own branch. currently I have a single python array and when I input my data tree and .append the list both branches are places in the first index of the list. so mylist[0] -> both points, as I operate on these points to grow the array, this continues, and when I feed the array out of python, the GH branch structure is preserved.

I would like to compare the branches to one another within python. I need to understand how to break up the input data tree within the code, and assign them to their own array.

Even better would be to create a 2D array from the data tree, assigning each branch a row and each branch item to a column.

any explanation or reference is appreciated.

this is my initial assignment code.

userIn = x
pt = rs.AddPoint(userIn)
pts = []
pts.append(pt)

Replies to This Discussion

Permalink Reply by Nico Azel on November 4, 2013 at 10:12pm

This might be a simpler way to ask the question

I am a trying to understand how python deals with GH data.

If I have a data tree with two branches, each containing 4 items as a input to a python component. What code is required to translate this into a 2D array with 2 rows and 4 columns? Does the type of data stored in the Items matter? If data types matter, lets assume that we are dealing with points.

If anyone knows of a reference that explains this or is willing to explains it would be much appreciated.

Permalink Reply by Nico Azel on November 4, 2013 at 10:22pm

seems i figured it out

import Rhino
#import grasshopper classes
import clr
clr.AddReference("Grasshopper")
from Grasshopper.Kernel.Data import GH_Path
from Grasshopper import DataTree

newlist = {}
newlist = x[:][:]
print newlist
print newlist[:][:]
A = newlist[:][:]

Permalink Reply by Giulio Piacentino on November 5, 2013 at 4:31am

Hi Nico

just make sure that you know what you are doing with this method, as Grasshopper datatrees contain slightly more information than simple lists of lists. For example, they can have gaps and the only way to assure that you are going through them as they are precisely intended is to explicitly go by each path, one at the time. See here for an example.

Btw, in the last release of ghPython, there is no need to add import clr / clr.AddReference()

I hope this helps,

Giulio
--

Giulio Piacentino
for Robert McNeel & Associates
giulio@mcneel.com

Permalink Reply by Mostapha Sadeghipour Roudsari on November 4, 2013 at 10:46pm

Hi Nico,

You can read the branches with a code similar to this. You need to set the input access to "tree access":

x.Branch(branchNumber)

In your case it should be something similar to this:

ptList1 = pts.Branch(0)

ptList2 = pts.Branch(1)

Permalink Reply by Vangel Kukov on January 6, 2014 at 7:05am

Hello, I am a bit confused here. When I read a branch with this method it outputs the type List[Object] and I cannot use the standard Python list methods on it like slice, pop, append. How do I cast this list into a regular Python list? Thanks.

Permalink Reply by djordje on January 6, 2014 at 8:51am

Can't you just take the items from List[object] and append them to a regular python list?

someList = x.Branch(1) #List[Object]

pythonList = [item for item in someList]

Permalink Reply by Anders Holden Deleuran on January 7, 2014 at 2:28am

The Python list() function will also do the trick:

someList = x.Branch(1) #List[Object]

pythonList = list(someList)

Permalink Reply by Nik Willmore on January 14, 2016 at 3:11pm

KEYWORDS: how to turn a Grasshopper tree into a Python list life-saving best answer ever.

Permalink Reply by Giulio Piacentino on January 7, 2014 at 1:32am

Yes - that is a .Net list, because Grasshopper is written in .Net so its SDK uses those classes. You can do as Djordje proposes if you prefer to get a normal Python list.

Thanks,

Giulio
--
Giulio Piacentino
for Robert McNeel & Associates
giulio@mcneel.com

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