Filter max 20 values from a list of integers

Question

I'd like to create a list maxValues containing top 20 values from a list of integers lst.

maxValues = []
for i in range(20):
  maxValues.append(max(lst))
  lst.remove(max(lst))

Is there a more compact code for achieving this task or even built-in function?

Answer 1

There's heapq.nlargest():

maxvalues = heapq.nlargest(20, lst)

From the doc:

heapq.nlargest(n, iterable, key=None)

Return a list with the n largest elements from the dataset defined by iterable. key, if provided, specifies a function of one argument that is used to extract a comparison key from each element in iterable (for example, key=str.lower). Equivalent to: sorted(iterable, key=key, reverse=True)[:n].

Or at the same way use heapq.nsmallest() if you want the smallest.

IMPORTANT NOTE from the doc:

The latter two functions [nlargest() and nsmallest()] perform best for smaller values of n. For larger values, it is more efficient to use the sorted() function. Also, when n==1, it is more efficient to use the built-in min() and max() functions. If repeated usage of these functions is required, consider turning the iterable into an actual heap.