If I have list of tuples like this:
my_list = [(\'books\', \'$5\'), (\'books\', \'$10\'), (\'ink\', \'$20\'), (\'paper\', \'$15\'), (\'paper\', \'$20\'), (\'pap
If your data is already grouped like you sample input, you can use itertools.groupby, grouping by each first element of the tuples and summing the prices in each group:
from itertools import groupby
from operator import itemgetter
my_list = [('books', '$5'), ('books', '$10'), ('ink', '$20'), ('paper', '$15'), ('paper', '$20'), ('paper', '$15')]
grouped = [(k, "${}".format(sum(int(s[1][1:]) for s in v)))
for k ,v in groupby(my_list, itemgetter(0))]
Output:
[('books', '$15'), ('ink', '$20'), ('paper', '$50')]
If it were not ordered you could call sorted groupby(sorted(my_list), itemgetter(0))
but changes the complexity to n log n
so a dict option may be better in that case.
You can also do the groupby on data
and forget building an intermediary list, csv.reader
will also split the data for you:
from itertools import groupby
from operator import itemgetter
from csv import reader
grouped = [(k, "${}".format(sum(int(s[1]) for s in v)))
for k, v in groupby(reader(data), itemgetter(0))]
You might be better also leaving the values as ints and formatting when you want to output. Also to handle floats cast to float not int:
from csv import reader
grouped = [(k, sum(float(s[1]) for s in v))
for k, v in groupby(reader(data), itemgetter(0))]
When you want to output you can add the dollar sign and also pad so you get nicely formatted output:
In [10]: "${:.2f}".format(1.0)
Out[10]: '$1.00'
This is fairly easy using a dictionary:
result={} #initialize an empty dictionary
for (type,cost) in my_list:
if type not in result.keys():
result[type]=int(cost[1:]) #add entry
else:
result[type]=result[type]+int(cost[1:]) #increment cost
#make dictionary a list again
dictlist=[]
for key, value in result.iteritems():
temp = [key,"$"+str(value)] #add dollar sign
dictlist.append(temp)
print dictlist
Edit: forgot two lines
You can use defaultdict to do this:
>>> from collections import defaultdict
>>> my_list = [('books', '$5'), ('books', '$10'), ('ink', '$20'), ('paper', '$15'), ('paper', '$20'), ('paper', '$15')]
>>> res = defaultdict(list)
>>> for item, price in my_list:
... res[item].append(int(price.strip('$')))
...
>>> total = [(k, "${}".format(sum(v))) for k, v in res.items()]
>>> total
[('ink', '$20'), ('books', '$15'), ('paper', '$50')]
You can simply use a dictionary to solve this problem.
my_list = [('books', '$5'), ('books', '$10'), ('ink', '$20'),
('paper', '$15'), ('paper', '$20'), ('paper', '$15')]
sums = {}
for item, price in my_list:
sums[item] = sums.get(item, 0) + int(price[1:])
print sums
And if you need list of tuples, just do
print sums.items()
And to get your the output you expect,
print [(item, '$' + str(price)) for item, price in sums.items()]
Update
If you have costs with floating point value, you can simply change int
to float
like this and rest of the code remains the same,
sums[item] = sums.get(item, 0) + float(price[1:])
Just for fun, a one-liner:
[(k,'$'+str(sum(int(e[1][1:]) for e in my_list if e[0]==k))) for k in set(map(lambda x:x[0], my_list))]
Don't actually do this.