1

Hi all I am having trouble trying to sum all the values in a list. I'm not sure if this is actually possible first. 

dL= list(csv.reader(input))
sL = dL [14247:14611]
a = [row[5] for row in sL[1:]] 
print a

This code is what I have so far and produces the result 

['5.0', '0.0', '0.0', '0.0', '0.0', '1.6', '4.4', '14.0', '0.0', '0.0', '0.8', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '95.6', '63.6', '0.0', '0.0', '0.0', '9.0', '0.0', '0.0', '0.0', '0.0', '20.2', '14.4', '1.6', '0.0', '7.6', '2.4', '0.0', '11.4', '0.0', '79.4', '60.4', '27.2', '', '1.8', '0.0', '0.0', '29.6', '67.6', '2.2', '0.0', '0.0', '0.0', '14.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '', '3.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '6.2', '0.0', '0.0', '0.0', '0.8', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '11.8', '2.4', '0.0', '0.0', '0.0', '0.4', '16.8', '8.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '2.6', '27.2', '77.0', '0.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '9.2', '2.6', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '1.6', '0.0', '0.0', '0.0', '0.0', '0.0', '6.8', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '', '', '', '', '', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '37.8', '0.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0']

The above list is not typed but produced by the function code. Does this affect the result?

Can anyone please assist me in showing me how to solve this problem and sum all these values in a code from this list. I believe I will have to join string to do so but am unsure. Can you please inform me whether this is possible to sum all these values of the list and if so how can I do it?

EDIT: 

THANKS FOR ALL THE HELP GUYS
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2
  • 1
    Note: The list has empty strings. Cannot be easily seen from this long list. Commented May 27, 2013 at 10:29
  • Regarding EDIT: Delete the a = ['']; and print the calculated sum not a. Commented May 27, 2013 at 12:52

3 Answers 3

Reset to default
5

I would use math.fsum for a more accurate sum:

>>> nums = ['5.0', '0.0', '0.0', '0.0', '0.0', '1.6', '4.4', '14.0', '0.0', '0.0', '0.8', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '95.6', '63.6', '0.0', '0.0', '0.0', '9.0', '0.0', '0.0', '0.0', '0.0', '20.2', '14.4', '1.6', '0.0', '7.6', '2.4', '0.0', '11.4', '0.0', '79.4', '60.4', '27.2', '', '1.8', '0.0', '0.0', '29.6', '67.6', '2.2', '0.0', '0.0', '0.0', '14.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '', '3.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '6.2', '0.0', '0.0', '0.0', '0.8', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '11.8', '2.4', '0.0', '0.0', '0.0', '0.4', '16.8', '8.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '2.6', '27.2', '77.0', '0.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '9.2', '2.6', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '0.2', '0.0', '0.0', '0.0', '0.0', '1.6', '0.0', '0.0', '0.0', '0.0', '0.0', '6.8', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '', '', '', '', '', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '37.8', '0.2', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0', '0.0']
>>> from math import fsum
>>> fsum(float(n or 0.0) for n in nums)
749.8

As opposed to

>>> sum(float(n or 0.0) for n in nums)
749.8000000000003

Using your code, a more efficient way of doing it without saving the whole file into memory at once:

from itertools import islice
dL= csv.reader(input)
sL = islice(dL, 14247+1, 14611)    
a = [row[5] for row in sL] 
print fsum(float(n or 0.0) for n in a)
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4 Comments

This is a nice code however my list is not actually typed by hand but created using the function. Will this result still work? I am trying to use the code but it doesnt work. Do i have to type the list out manually?
@user2423678 you may be required to use other parts of the list in your code, so then it's best to store it all in memory at once, however you didn't give any information regarding that in the question statement
How would i store that in memory as you say in order to use the list to sum the values?
@user2423678 I was referring to your original code which stores the whole list in memory
2

You can sum all numbers with sum but need to convert the strings to floats before and check for empty strings:

sum(float(x) for x in a if x)
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8 Comments

this doesn't work since the input has empty strings, try float('')
There's an if in the comprehension (now).
Works for me a = [''];sum(float(x) for x in a if x) gives 0.0.
in terms of this the list isnt actually typed it is produced by the function. Does this still work because it doesnt work for me
It does not matter how the list comes about. As long as a is a list of strings it works, no matter if you type it in, read it from a file or use some other way to generate it.
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0

This also works:

reduce(lambda x,y:x+y, map(float, filter(lambda x:x!='', a)))
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1 Comment

A rather convoluted form of: sum(map(float, filter(None, a))) ?

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