Union in Sage/Python

Question

I have a list of lists (that might have any number of lists as entries) and want to find the union of this list (as a set) in Sage. I would think there is a short existing command already but I was not able to find it.

Here an example:

W=[[2, 1], [2], [3, 1], [1]]
T=W.union()
display(W)
display(T)

The desired output is T=[1,2,3] but it seems the command "union" does not work.

score 2 · Accepted Answer · answered Aug 03 '21 at 13:10

2

You can use set().union()

W=[[2, 1], [2], [3, 1], [1]]
T=set().union(*W)
print(W)
print(T)

answered Aug 03 '21 at 13:10

Lakshan Costa

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Thank you. But why do we need a star before the W? – Mare Aug 03 '21 at 14:00
@Mare https://stackoverflow.com/questions/2921847/what-does-the-star-and-doublestar-operator-mean-in-a-function-call This explains it very well – Lakshan Costa Aug 03 '21 at 14:06

Union in Sage/Python

1 Answers1