具有嵌套列表的列表理解

Question

Would like to ask question related to nested lists in Python.

I have a nested list

list_1 = [[1,3,0,1], [1,1,0,2,3,0,4,], [2,1,2,2,3,4]]

I want to perform rounding and dision operation on nested list but keep it grouped as it is now (to make it more clear I need to flatten list perform operations and that unflatten it again in same groups).

For example the result for list 'list_1' after division by 2 shoud be

list_2 = [[0.5,1.5,0,0.5],[0.5,0.5,0,1,1.5,0,2],[1,0.5,1,1,1.5,2]]

The code I use to perform this for signle list is below:

list_2 = [round(b,2) for b in [a / 2 for a in list_1]]

Could you please suggest way to solve this issue. Currently I am getting error

"unsupported operand type(s) for /: 'list' and 'float'"

Thank you.

Answer 1

Fixing your code -

[[j / 2. for j in i] for i in list_1] 

If you're worried about performance, you could multiply by .5 instead of dividing by 2 (you may not see significant differences considering this is a quadratic solution, but it should count for something ).

[[j * .5 for j in i] for i in list_1] 

The docs have a section just for Nested List Comprehensions , please consider having a read through.