Python:List Addition

Question

I have two lists like below.i am getting this from database

EmpID = Assign.objects.select_related().filter(pName=selProject).filter()
    .order_by('laEmpNum').values_list('laEmpNum', flat=True)

TotDur = Assign.objects.select_related().filter(pName=selProject).order_by('laEmpNum')
    .values_list('duration', flat=True)

EmpID = [u'1046', u'1046', u'1046', u'8008', u'8008', u'8011'] 

TotDur = [0.0, 2.0, 2.5, 0.0, 2.7, 1.2]

If EmpIDs are same then corresponding values in TotDur should collect and add(sum).

ResOne = 0.0 + 2.0 + 2.5    i.e 4.5
ResTwo = 0.0+2.7            i.e 2.7
ResThr = 1.2                i.e 1.2

How to do this in Python.

Yuval Adam · Accepted Answer · 2012-11-17 09:39:33Z

3

defaultdict is a good data structure to use, for int fields it assumes the value 0 for new keys, and allows for easy bucket collection:

from collections import defaultdict
d = defaultdict(int)
for i, j in zip(EmpID, TotDur):
    d[i] += j
print d # defaultdict(<type 'int'>, {u'8008': 2.7, u'1046': 4.5, u'8011': 1.2})

answered Nov 17, 2012 at 9:39

Yuval Adam

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3 Comments

Ashwini Chaudhary Over a year ago

How's this different from my answer?

Yuval Adam Over a year ago

It isn't, I didn't notice yours until I posted mine ;)

Phil H Over a year ago

@AshwiniChaudhary: Why does it need to be different? It does explain the int behaviour explicitly, which I found useful.

Abhijit · Accepted Answer · 2012-11-17 10:01:21Z

2

If the elements are in order as you have shown in your example, you can use itertools.groupby

from itertools import groupby
from operator import itemgetter
[(k , sum(e for _,e in v)) for k,v in groupby(zip(EmpID, TotDur), itemgetter(0))]
[(u'1046', 4.5), (u'8008', 2.7), (u'8011', 1.2)]

infact you don't need to create two separate list and zip it later

Emp_TotDur = Assign.objects.select_related().filter(pName=selProject).filter()
    .order_by('laEmpNum').values_list('laEmpNum', 'duration')

[(k , sum(e for _,e in v)) for k,v in groupby(Emp_TotDur, itemgetter(0))]

edited Nov 17, 2012 at 10:01

answered Nov 17, 2012 at 9:42

Abhijit

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Comments

Ashwini Chaudhary · Accepted Answer · 2012-11-17 09:37:25Z

2

you can use defaultdict:

In [60]: from collections import *

In [61]: EmpID = [u'1046', u'1046', u'1046', u'8008', u'8008', u'8011']

In [62]: TotDur = [0.0, 2.0, 2.5, 0.0, 2.7, 1.2]

In [63]: d=defaultdict(int)

In [64]: for x,y in zip(EmpID,TotDur):
    d[x]+=y
   ....:     

In [65]: d
Out[65]: defaultdict(<type 'int'>, {u'8008': 2.7, u'1046': 4.5, u'8011': 1.2})

or simply dict:

In [70]: d=dict()

In [71]: for x,y in zip(EmpID,TotDur):
    d[x]=d.get(x,0)+y
   ....:     

In [72]: d
Out[72]: {u'1046': 4.5, u'8008': 2.7, u'8011': 1.2}

answered Nov 17, 2012 at 9:37

Ashwini Chaudhary

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Comments

Lucas Hoepner · Accepted Answer · 2012-11-17 09:39:34Z

0

You can do it like this

l1 = [1,1,2,3,3]
l2 = [1,2,3,4,5]
last_val=l1[0]
sum=0
list=[]
for pair in zip(l1,l2): 
    if pair[0]!=last_val:
        print(sum)
        list.append(sum)
        sum=0
    last_val=pair[0]
    sum+=pair[1]
list.append(sum)
print(list)

answered Nov 17, 2012 at 9:39

Lucas Hoepner

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Emil Vikström · Accepted Answer · 2012-11-17 09:40:47Z

0

You can zip the two lists, which pairs the elements of the first to the elements of the second into tuples. Then loop over them and use the first part of the tuple as keys in a dictionary:

EmpID = [u'1046', u'1046', u'1046', u'8008', u'8008', u'8011']
TotDur = [0.0, 2.0, 2.5, 0.0, 2.7, 1.2]
Result = {}

for (key, value) in zip(EmpID, TotDur):
    if not key in Result:
        Result[key] = value
    else:
        Result[key] += value

# Print the result
for (key, value) in Result.items():
    print key, value

You may want to use an OrderedDict if you want to preserve the order of the Emps

answered Nov 17, 2012 at 9:40

Emil Vikström

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Comments

tozlu · Accepted Answer · 2012-11-17 09:44:24Z

0

Try this, it puts sum of all corresponding id's values to a list, later you can access the list with empId and see its sum.

finalList = []
lastEmpId

for index, emp in enumarate(EmdIP):
    if lastEmpId == emp:
        finalList[lastEmpId] += TotDur[index]
    else:
        finalList[lastEmpId] = TotDur[index]
    lastEmpId = emp;

print finalList

answered Nov 17, 2012 at 9:44

tozlu

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Comments

raton · Accepted Answer · 2012-11-17 18:33:12Z

0

    python 3.2
    res=[]
    for i in set(ID):
         b=[]
         for x,y in enumerate(ID):
              if i==y: b.append(T[x])
    res.append(sum(b))

edited Nov 17, 2012 at 18:33

answered Nov 17, 2012 at 18:15

raton

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