Sort Points by Y in Python

[flokart]

Hi all,

how can a pointlist be sorted by Y Value?

Thanks

[Helvetosaur]

There are a number of ways, you could use rs.SortPoints() or something like the following:

#(assuming pts is a list of 3D points)
pts_sort_y = [item[1] for item in sorted([(pt.Y,pt) for pt in pts])]

[AndersDeleuran]

I shared two of the methods I tend to implement here:

Grasshopper python command combining two if commands

See my reply here for two general methods for sorting in Python based on keys (you’ll want method 1 likely): Also, note that a “safe” method for checking if two values (or points) are identical, is to subtract the two and check that the result is smaller than some acceptable tolerance value (for points, calculate the distance between the two and check this is smaller than your tolerance).

[flokart]

Thanks for the examples.

the List comprehension method is nice.

[AndersDeleuran]

@flokart

the List comprehension method is nice

You don’t need the nested loop/list comprehension, can get there with just sorted():

181011_SortPointsByY_00.gh (4.1 KB)

[flokart]

Thanks a lot for this example…

i have a lot of problems to understand the key in the sort method.
Your example is easy to understand.

[AndersDeleuran]

The key parameter defines what to sort by and the lambda is just an inline function (in this case, one that returns the Y component of a point). One can usually find good sources on Google for general Python patterns (like sorting etc): https://wiki.python.org/moin/HowTo/Sorting

[germyrinn]

The key parameter in list.sort() method specifies a function that will be called on each list item before making comparisons. If you want your own implementation for sorting , you can use key parameter as an optional parameter.

def keyArgs(args):
    return args[1]
numList = [('Five', '5'), ('Two', '2'), ('Four', '4'), ('One', '1'), ('Three','3')]
numList.sort(key=keyArgs)
print(numList)