Pythonic way to find value in 2D list?

user_7748291 0
Viewed 2023

With numpy array, you can check a specific column with slicing, i.e. array[:, 0]. For a list, checking whether a 2D element is inside is as simple as ["one", "two"] in some_list. However, just looking if "one" is present requires one to iterate through the elements, i.e. ["one" == item[0] for item in some_list].

I largely prefer numpy array except that my array needs to be modified (adding at the end and removing values). I like to work with list because they are very simple to work with. I am considering dataframe but I feel like I should be able to find some clever and efficient way to this kind of operation using a list.

python-3.x list python
2 Answers

To check whether item exists at any position in a 2D list list_of_lists, you can do

any(item in sublist for sublist in list_of_lists)

Note, unlike the list-flattening idea of another answer, this solution doesn't require any extra memory to be used.

user_10089660

Not sure if this is what you're asking, but if all you want is to know if an element exists inside a list of lists l, you can flatten l and use the operator in as below:

>> l = [["one", "two"], ["three", "four"]]
>> one_is_in_l = "one" in [item for sublist in l for item in sublist]
>> print(one_is_in_l)
True

You can also use numpy just to do the check with:

>> l = [["one", "two"], ["three", "four"]
>> one_is_in_l = "one" in np.array(l)
>> print(one_is_in_l)
True
user_82680980
Related