CODEWITHSUNDEEP
pythonlistsorting
Optimesh
Optimesh

Reputation: 2857

Sort (and sorted) not sorting

I have a data file that's built the following way:

source_id, target_id, impressions, clicks

on which I add the following columns:

Lower/Upper bound are calculated values (it's irrelevant to my question, but for the curious ones these are the bounds for the Wilson confidence interval.

The thing is, I'm trying to sort the list by the lower bound (position = 6), descending. Tried several things (sort/sorted, using lambda vs. using itemgetter, creating a new list w/o the header and try to sort just that) and still it appears nothing changes. I have the code below.

import csv
from math import sqrt
from operator import itemgetter

#----- Read CSV ----------------------------------------------------------------
raw_data_csv  = open('rawdile', "rb")
raw_reader = csv.reader(raw_data_csv)

#  transform the values to ints.
raw_data = []
for rownum,row in enumerate(list(raw_reader)):
    if rownum == 0:                                                             # Header
        raw_data.append(row)
    else:
        r = []                                                            # Col header
        r.extend([int(x) for x in row])                                     # Transforming the values to ints
        raw_data.append(r)



# Add cols for pairs (as tuple) and CTR
raw_data[0].append("pair")


for row in raw_data[1:]:
    row.append((row[0],row[1]))         # tuple
#    row.append(float(row[3])/row[2])    # CTR



# ------------------------------------------------------------------------------


z = 1.95996398454005


def confidence(n, clicks):

    if n == 0:
        return 0
    phat = float(clicks) / n
    l_bound = ((phat + z*z/(2*n) - z * sqrt((phat*(1-phat)+z*z/(4*n))/n))/(1+z*z/n))        # lower bound
    u_bound = ((phat + z*z/(2*n) + z * sqrt((phat*(1-phat)+z*z/(4*n))/n))/(1+z*z/n))        # upper bound
    return phat, l_bound, u_bound


raw_data[0].extend(["CTR","Lower Bound","Upper Bound"])


for row in raw_data[1:]:
    phat, l_bound, u_bound  = confidence(row[2],row[3])
    row.extend([phat, l_bound, u_bound])



# raw_data[1:].sort(key=lambda x: x[6], reverse=True) 

sorted(raw_data[1:], key=itemgetter(6), reverse=True)



outputfile= open('outputfile.csv', 'wb')
wr = csv.writer(outputfile,quoting = csv.QUOTE_ALL)

wr.writerows(raw_data)


raw_data_csv.close()
outputfile.close()

Can anybody tell why? Thanks!

Upvotes: 0

Views: 314

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1124928

You are sorting a slice in one attempt (which creates a new list object), and in your other attempt you ignore the return value of sorted().

You cannot sort part of a list like that; create a new list by concatenating instead:

rows = rows[:1] + sorted(raw_data[1:], key=itemgetter(6), reverse=True)

Upvotes: 2

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