python - Deleting list elements based on condition

44
votes

I have a list of lists: [word, good freq, bad freq, change_status]

list_1 = [['good',100, 20, 0.2],['bad', 10, 0, 0.0],['change', 1, 2, 2]]

I would like to delete from the list all elements which don't satisfy a condition.

So if change_status > 0.3 and bad_freq < 5 then I would like to delete that the elements corresponding to it.

So the list_1 would be modified as,

list_1 = [['good',100, 20, 0.2],['bad', 10, 0, 0.0]]

How do I selective do that?

2
pythonlistelements
I think he meant > for the first one. But actually your comment is wrong. x < a and x < b with a < b results in x < a, not in x < b as you said. - ThiefMaster
I get good and change not good and bad for those conditions -- bads bad_freq is 0 and its change_status is 0.0. - agf

2 Answers

57
votes
list_1 = [['good',100, 20, 0.2],['bad', 10, 0, 0.0],['change', 1, 2, 2]]
list_1 = [item for item in list_1 if item[2] >= 5 or item[3] >= 0.3]

You can also use if not (item[2] < 5 and item[3] < 0.3) for the condition if you want.

17
votes

Use the filter function with an appropriate function.

list_1 = filter(lambda x: x[3] <= 0.3 and x[2] < 5, list_1)

Demo:

In [1]: list_1 = [['good',100, 20, 0.2],['bad', 10, 0, 0.0],['change', 1, 2, 2]]
In [2]: filter(lambda x: x[3] <= 0.3 and x[2] < 5, list_1)
Out[2]: [['bad', 10, 0, 0.0]]

Note that good doesn't satisfy your condition (20 < 5 is false) even though you said so in your question!

If you have many elements you might want to use the equivalent function from itertools:

from itertools import ifilter
filtered = ifilter(lambda x: x[3] <= 0.3 and x[2] < 5, list_1)