How do I round numbers in a list?

[Miguel Valenzue]

I want to round a list of numbers to basically remove all the decimal places or even just convert them to integers.

So this is what I've tried and I just can't get this to work.

myList = [10.5,25.1,350.6,4,5,6] #declare my list
for i in range(len(myList)):
    myList[i] == round(i,0)  #tries to round all numbers.
print myList
 
#other Attempt
for i in range(len(myList)):
    myList[i] == int(i)  #tries to make i into an integer
print myList
 
#other attempt
 
for i in myList:
     int(i)
 
 

I'm just not getting this.

Thanks

[zmbd]

So what error message are you getting?
So what output, if any, are you getting?
Hint: round(i,0) returns a double so if you want to round and then return the integer part only...

-z

[Miguel Valenzue]

Okay, here's the code again:

myList = [10.5,25.1,350.6,4,5,6]
 
for i in myList:
    int(i)
 
print myList
 
for i in myList:
    round(i)
 
print myList
 
for i in range(len(myList)):
    myList[i] == round(i,0)
 
print myList
 

Here's my output

[10.5, 25.1, 350.6, 4, 5, 6]
[10.5, 25.1, 350.6, 4, 5, 6]
[10.5, 25.1, 350.6, 4, 5, 6]

My desirec output is
[11, 25, 351, 4, 5, 6]

No errors. Just doesn't do anything.
When you say it returns a double. clueless on what that implies.

[zmbd]

Returns a data type of "double" vs integer, long, etc..
Data types are covered in most good books and you can google on them as related to python/ruby/vba/.net etc...

My hint has the solution.

-z

[Miguel Valenzue]

I will call you Gollum from now own, master of riddles. ;)
Okay, I understand double.
So if round is returning a double, then I need to convert that into an integer.

I've tried that (at least I think) with this code.

for i in myList:
    int((round(i)))
 
print myList

But on a deeper level, is my logic right? to redefine the numbers (long) in a list by just using the for loop?

[bvdet]

In your first example, you are using the comparison operator "==" when you should be using the assignment operator "=". Also, you should combine int() and round() to achieve the desired output.

>>> int(round(12.5, 0))
13
>>> x == int(round(12.5, 0))
False
>>> x = int(round(12.5, 0))
>>> x
13
>>> 

A list comprehension is the easiest way.

>>> x = [1,2,3,11.5]
>>> newlist = [int(round(n, 0)) for n in x]
>>> newlist
[1, 2, 3, 12]
>>> 

[zmbd]

bvdet
sigh... you let 'em off the hook. :(
-z

[bvdet]

Sorry about that zmbd. If he was going to "get it" he already would have.

[Miguel Valenzue]

Well, first of all, thanks both of you. I appreciate your time.
But after looking at the way I was approaching it, I want to learn a bit more here.
I got the code to work so now my vector multiplication that I was going for is complete.

But this was my thought process.

If I put

int(12.5,0)
 

in the command line of python, it returns 13

So that was fine with me. I get that.

But this was my thinking.
If I have a list, I can do something real basic like this

myList =[4,3,5,6,1]
 
for range in (len(myList)):
     i=*3
 
 

That returns a new list of
12,9,15,6,1

So my thought process was, why can't I just use the round or integer function within the same statement such as

for range in (len(myList)):
     i=int(i)
 

But when I do this, it returns a number like 2.000000001 or something like that.

Anyhow, that's what I don't get so as part of my learning experience, can you help me understand what is happening? I see that round returns a double like you said, but how does that double go back to being an int?

I mean, why doesn´t the following code work?

for range in (len(myList)):
     i=int(round(i,0))
 
 

thanks again
Oh, and bvdet,
I didn´t know you could use list comprehension like that.
I redid all my code and cut it down by about 25% with that new found knowledge.

[bvdet]

In your for loop, range is used as a temporary identifier for the expression len(myList), which returns an integer. You cannot iterate on an integer. Also, you will mask the built-in function range(). I think you meant to do this:

>>> myList = [10.2, 12.9]
>>> for i in range(len(myList)):
...     myList[i]=int(round(myList[i],0))
...     
>>> myList
[10, 13]
>>> 

The temporary identifier i can be used as the index for getting each list element and reassigning the element at that index. Identifier i will retain the last value assigned to it. Built-in function range() returns a list.

>>> range(len(myList))
[0, 1]
>>> i
1
>>> 

HTH