Creating a list with two different numbers

Question

I have 2 numbers x and y. x for example is 1.5, and y is 1.5 I need to create a list of lists with 8 different values.

[[0.5,0.5],[0.5,1.5],[0.5,2.5],
[1.5,0.5],[1.5,1.5],[1.5,2.5],
[2.5,0.5],[2.5,1.5],[2.5,2.5]]

[1.5,1.5] #needs to be removed from the above list.

How can I do this in python 3 using different x and y values? x and y will always be numbers between 1 and 10. But they will be 1.5 or 2.5 or 3.5 etc.

Can x and y be any floating point number as long as it's between 1 and 10? ie. 2.452, 2.01, 6.42. Or will it only ever be .5? — Yep_It's_Me, Jun 04 '14 at 01:10
So you have a list of [x, y], and you want to remove that list from the list of lists, but only if x and y are the same? — Yep_It's_Me, Jun 04 '14 at 01:12
I want to make the top list the one with a len of 9. But, the list [x,y] where x and y are the variables x and y, i want gone. So its a list of len 8. And, no x and y can be different. for eg. x may = 4.5 while y may equal 2.5 — user3670654, Jun 04 '14 at 01:16
You probably shouldn't have described the removal conditions as "When x and y are the same" in your post. — user2357112, Jun 04 '14 at 01:26

A.J. Uppal · Accepted Answer · 2014-06-04T01:42:00.653

1

Try using the following list comprehension:

items = [[a, b] for a in items for b in items if x != a or y != b]

As such:

>>> x = 1.5
>>> y = 1.5
>>> items = [x-1, x, x+1]
>>> items = [[a, b] for a in items for b in items if x != a or y != b]
>>> items 
[[0.5, 0.5], [0.5, 1.5], [0.5, 2.5], [1.5, 0.5], [1.5, 2.5], [2.5, 0.5], [2.5, 1.5], [2.5, 2.5]]
>>>

Edit:

Or, if list comprehension is too confusing, you can just change it to nested for loops:

for i in items:
    for j in items:
        if i != x or j != y:
            cp.append([i, j])

This runs as:

>>> x = 1.5
>>> y = 1.5
>>> items = [x-1, x, x+1]
>>> cp = []
>>> for i in items:
...     for j in items:
...         if i != x or j != y:
...             cp.append([i, j])
... 
>>> items = cp
>>> items
[[0.5, 0.5], [0.5, 1.5], [0.5, 2.5], [1.5, 0.5], [1.5, 2.5], [2.5, 0.5], [2.5, 1.5], [2.5, 2.5]]
>>>

edited Jun 04 '14 at 01:42

answered Jun 04 '14 at 01:28

A.J. Uppal

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Would there be an easier way to do this? I haven't read up about list comprehension. – user3670654 Jun 04 '14 at 01:36
You could write it out without list comprehension, (ie. in multiple lines with nested for loops) if that makes it easier to understand? – Yep_It's_Me Jun 04 '14 at 01:37
@user3670654 the `a` and `b` are the ones being added to the list. – A.J. Uppal Jun 04 '14 at 01:43
Why do you need to go items = cp – user3670654 Jun 04 '14 at 01:44
@user3670654 you don't but now the results are stored in `items`. However, you can remove that and have the results be stored in `cp`. – A.J. Uppal Jun 04 '14 at 01:45
@aj8uppal but without items = cp, items is still [x-1, x, x+1] and cp is now the list I want? – user3670654 Jun 04 '14 at 01:51
@user3670654 yes, that is exactly it. – A.J. Uppal Jun 04 '14 at 01:51
@user3670654 if this answer helped you do you mind accepting it by clicking on the green check next to my answer? Fill disclosure: it gives you +2 reputation :) – A.J. Uppal Jun 04 '14 at 01:57
@aj8uppal it isn't quite working properly. when i put x as 3.5 and y as 1.5 – user3670654 Jun 04 '14 at 02:31
Yes, because it is creating a list of all the permutations of `[2.5, 3.5, 4.5]`. In your question, you stated that x and y are equal, which is what I designed this code to deal with. – A.J. Uppal Jun 04 '14 at 02:36

score 0 · Answer 2 · answered Jun 04 '14 at 01:15

0

Try this:

values = [0.5, 1.5, 2.5]
[[x, y] for x in values for y in values if x <> y]

Output:

[[0.5, 1.5], [0.5, 2.5], [1.5, 0.5], [1.5, 2.5], [2.5, 0.5], [2.5, 1.5]]

answered Jun 04 '14 at 01:15

Brionius

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I need a list of len 8. – user3670654 Jun 04 '14 at 01:17
1

Your filter clause removes too much. Also, why the `<>` syntax? It's old, weird, and gone in Python 3. – user2357112 Jun 04 '14 at 01:21

score 0 · Answer 3 · edited May 23 '17 at 10:32

0

Check out this question.

To remove from a list:

list_to_remove = [x, y]
list_of_lists = [[0.5,0.5],[0.5,1.5],[0.5,2.5],
                [1.5,0.5],[1.5,1.5],[1.5,2.5],
                [2.5,0.5],[2.5,1.5],[2.5,2.5]]
list_of_lists.remove(list_to_remove)

Keep in mind that this will raise an exception if list_to_remove is not in list_of_lists. To catch this, you need:

list_to_remove = [x, y]
list_of_lists = [[0.5,0.5],[0.5,1.5],[0.5,2.5],
                [1.5,0.5],[1.5,1.5],[1.5,2.5],
                [2.5,0.5],[2.5,1.5],[2.5,2.5]]

try:
    list_of_lists.remove(list_to_remove)
except:
    print "{0} is not in list_of_lists".format(str(list_to_remove))

edited May 23 '17 at 10:32

Community

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answered Jun 04 '14 at 01:18

Yep_It's_Me

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I don't need to remove the entry. I need a list created with all those numbers according to x and y. [x,y] can be removed later. – user3670654 Jun 04 '14 at 01:21
What do you mean 'according to x and y'? Does this question have anything to do with removing from the list? – Yep_It's_Me Jun 04 '14 at 01:26
I don't need anything removed, I need the list created. I can't figure out an algorithm to create a list like that. – user3670654 Jun 04 '14 at 01:28
Sorry. I misunderstood your question. Perhaps it needs to be rephrased? – Yep_It's_Me Jun 04 '14 at 01:31

Creating a list with two different numbers

3 Answers3

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