CODEWITHSUNDEEP
pythonarraysvectorrounding
cavezonk
cavezonk

Reputation: 49

How to round values of a vector array

I'm working on a Python code and I need to round the values of this following array:

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

And finally get: 

 P= [[3, 4, 2],
     [5, 2, 2],
     [3, 3]]

I tried the following method but it doesn't work.

  for i in range(len(P)):
    P[i] = int(round(P[i], 0))

Upvotes: 2

Views: 1004

Answers (1)

Patrick Artner
Patrick Artner

Reputation: 51643

You can use list comprehensions:

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

P2 = [[int(round(x,0)) for x in y] for y in P]
# P is your list of lists
# y is each inner list
# x is each element in y
# rounding logic is as yours

print(P2)

Output:

 [[3, 4, 2], [5, 2, 2], [3, 3]]

Edit: 2.7 and 3.6 behave differently - I used a 2.7 shell.

See round()

Note The behavior of round() for floats can be surprising: for example, round(2.675, 2) gives 2.67 instead of the expected 2.68. This is not a bug: it’s a result of the fact that most decimal fractions can’t be represented exactly as a float. See Floating Point Arithmetic: Issues and Limitations for more information.

You can fix it by creating your own round-Method:

def myRounder(num):
    return int(num)+1 if num - int(num) >= 0.5 else int(num)    

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

P2 = [[int(myRounder(x)) for x in y] for y in P]
# P is your list of lists
# y is each inner list
# x is each element in y
# rounding logic is as yours

print(P2)

This will lead to the same results on 2.7 and 3.x.

Upvotes: 2

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