In a sorted list of lists, remove elements from index number n that already exist in indexes from 0 to n-1

Lists-Logic
1

Hi,
I have a list of lists containing several elements. I would like to be able to go through every list and remove the elements that are already contained in the previous lists. So for example:
List with Index 0 - Does not get affected
List with Index 1 - All elements that are already in list with index 0 get removed
List with Index 2 - All elements that are already in lists with indexes 0 and 1 get removed
And so on…

image

Do I need python for this?

2

Python would certainly make short work of this, but you might also be able to get something with ootb nodes and a little list magic.

As for python, you would just keep a list of existing elements and check every new element against that list. If the element already exists you ignore it, otherwise it gets added back in to your output list.

3

Thanks @Nick_Boyts . I’ll try Python then…
I’m not very versed in Python (only in C#). However, I think the solution might lie somewhere along these lines:
# The inputs to this node will be stored as a list in the IN variables.
dataEnteringNode = IN

# Place your code below this line
ElementsList = IN[0]
outputElements = []
totalElements = []

for elements in ElementsList:
	tempElements = []
	for element in elements:
		if element not in totalElements:
			tempElements.append(element)
	totalElements.append(tempElements)
	outputElements.append(tempElements)
	
	
# Assign your output to the OUT variable.
OUT = outputElements

However, my output is the same as my input. What am I doing wrong?

4

You’re pretty close. Try appending the element directly to totalElements, rather than within a list. This means you’ll also want it under the same loop.

5

Thank you! Almost there now:

for ElementsList in ElementsLists:
	tempElements = []
	for element in ElementsList:
		if element not in totalElements:
			outputElements.append(element)
		totalElements.append(element)

	
	
# Assign your output to the OUT variable.
OUT = outputElements

image

The only problem now is that I’m breaking the list structure that I need to keep! How would I keep the original list’s structure?

6

That was already working. You just needed to adjust totalElements, like this:

# Place your code below this line
ElementsList = IN[0]
outputElements = []
totalElements = []

for elements in ElementsList:
	tempElements = []
	for element in elements:
		if element not in totalElements:
			tempElements.append(element)
	        totalElements.append(element)
	outputElements.append(tempElements)
	
	
# Assign your output to the OUT variable.
OUT = outputElements
7

silly me! working perfectly now, thank you so much!

8

And just for fun, here’s an ootb solution.

image
image1467×453 103 KB

There are probably better ones, but this is what I came up with on a Monday morning.

9

That’s waaay too much magic! :grin: