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A small example. I have two lists with numbers, ra and dec here. I have a third list that also has some numbers, quad here.

What I want to do is to remove those values of ra and dec that are in quad. 

>>> ra = [1,1,1,2,3,4,5,6,7,8]
>>> dec = [1,2,3,4,5,6,7,7,7,7]
>>> quad = [1,2,3,1,2,3]
>>> new_ra = []
>>> new_dec = []
>>> for a,b in zip(ra,dec):
        if ((a not in quad) & (b not in quad)):
            new_ra.append(a)
            new_dec.append(b)

So here you would expect:

new_ra = [4,5,6,7,8]

and 

new_dec = [4,5,6,7,7,7]

How ever, I get:

new_ra = [4,5,6,7,8]

as expected, BUT, 

new_dec = [6,7,7,7,7]

Why is this so? What is wrong with my loop?

P.S. I am following the same method as in THIS QUESTION, but my second list does not give me the proper answer.

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Srivatsan
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  • By the way `&` is bitwise `AND`, you want to use the keyword `and` for logical `AND` – Cory Kramer Jul 16 '15 at 14:35
  • I am following the same method, but my second list does not give me what I want!!! What is wrong here?? – Srivatsan Jul 16 '15 at 14:35
  • When `b` is equal to 4 `a` is equal to `2`. You add elements to `new_ra` and `new_dec` lists only when `a` is not in `quad` _and_ `b` is not in `quad`. It means, that `4` will never be added to `new_dec` – Konstantin Jul 16 '15 at 14:38
  • @CoryKramer: I should say that `and` does not make a difference here and I get the same results – Srivatsan Jul 16 '15 at 14:38
  • @Alik: So how do I achieve it if I want it for remove for both the lists? – Srivatsan Jul 16 '15 at 14:40

1 Answers1

5

Why don't you use a simple list comprehension? 

new_ra = [v for v in ra if v not in quad]
new_dec = [v for v in dec if v not in quad]
clemtoy
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