Python中如何对二维数组的数值进行四舍五入取整？

Hey there! Let's sort out that rounding issue with your 2D array. The problem in your original code is that you're trying to apply round() to an entire sublist (P[i]) instead of each individual element inside the sublist. round() only works on single numeric values, not lists—so that's why you ran into errors.

Why Your Original Code Failed #

Your line P[i] = int(round(P[i], 0)) tries to round the whole sublist (like [3.2, 3.7, 2.1]) at once, which Python doesn't allow. You need to iterate through each number in every sublist to apply the rounding logic correctly.

Solution 1: Nested Loops (Explicit & Easy to Follow) #

If you prefer a straightforward, readable approach, use nested loops to go through each sublist and then each element inside it:

P = [[3.2, 3.7, 2.1], [4.5, 2.1, 2.3], [3.1, 2.5]]

for i in range(len(P)):
    rounded_sublist = []
    for num in P[i]:
        # Use int(num + 0.5) here to get traditional 0.5-up rounding (matches your expected output)
        rounded_num = int(num + 0.5)
        rounded_sublist.append(rounded_num)
    P[i] = rounded_sublist

print(P)  # Output: [[3, 4, 2], [5, 2, 2], [3, 3]]

Solution 2: List Comprehension (Pythonic & Concise) #

For a cleaner, more idiomatic Python solution, use a nested list comprehension to process all elements in one line:

P = [[3.2, 3.7, 2.1], [4.5, 2.1, 2.3], [3.1, 2.5]]

# Nested comprehension to round each element with traditional 0.5-up logic
P = [[int(num + 0.5) for num in sublist] for sublist in P]

print(P)  # Output: [[3, 4, 2], [5, 2, 2], [3, 3]]

Quick Note on Rounding Behavior #

Python's built-in round() uses bankers rounding, which rounds numbers ending in 0.5 to the nearest even integer (e.g., round(4.5) becomes 4, round(2.5) becomes 2). Since your expected output wants 4.5 → 5 and 2.5 → 3, using int(num + 0.5) (for positive numbers) gives you that classic "round up on 0.5" behavior you need.

内容的提问来源于stack exchange，提问作者cavezonk