Remove all elements except string from list

Question

I have a list which looks like this [[{a:7},"1",{x:0.25},"2"],[{y:0.25,x:1.5},"4"],[{y:-0.75},"3"]] and i want to remove everything that isn't a string from the list while still keeping the "shape" of the list so the output should look like this [["1", "2"], ["4"], ["3"]] . How can i do this?

Answer 1

To create new list with required values, you can use list comprehension:

given = [[{a: 7}, "1", {x: 0.25}, "2"], [{y: 0.25, x: 1.5}, "4"], [{y: -0.75}, "3"]]
new_data = [[e for e in inner if isinstance(e, str)] for inner in given]

This means: "create new list of lists, where inner items are only string values".

If you need to modify given list inplace, the following should do:

given = [[{a: 7}, "1", {x: 0.25}, "2"], [{y: 0.25, x: 1.5}, "4"], [{y: -0.75}, "3"]]
for i, inner in enumerate(given):
    given[i] = [e for e in inner if isinstance(e, str)]

Using pop or del in such context is not advisable, because a) it changes list length during iteration (and is bug prone), and b) it is less efficient.