How Can We Efficiently Partition a List Based on a Conditional Filter?

Efficient List Partitioning Based on Conditional Filtering

Consider the need to split a list into two sublists based on a condition. A naive approach would entail iterating over the list twice, once for each sublist. Seeking an efficient and elegant alternative, we explore several options.

One approach involves manually iterating over the list and dynamically appending each element to the appropriate sublist based on the conditional check. This is demonstrated in the code below:

good, bad = [], []
for x in mylist:
    (bad, good)[x in goodvals].append(x)

In this code, the (bad, good) expression evaluates to either bad or good depending on the boolean value of x in goodvals. The append() method of the selected sublist is then invoked to add the current element.

By eliminating the need for multiple iterations and using concise list comprehensions, this approach offers both performance and code readability benefits over the two-iteration implementation.

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