unable to enter for loop in python

Question

Here is my data.csv

a,1,1-Jan-2017
a,2,3-Jan-2017
a,4,14-Feb-2017
b,21,1-Dec-2016
b,7,28-Nov-2016

My target is to print below as final list. Format is unique(first_column),no.of occurences

a,3
b,2

Written below python script but unable to enter second block to print 'second block' although the same logic works fine in previous loop.

import csv

with open('/home/user/python/data.csv') as csvfile :
    DataCaptured = csv.reader(csvfile,delimiter=',')
    UniqueValues = []
    FinalList = []

    for row in DataCaptured :
            if row[0] not in UniqueValues :
                    UniqueValues.append(row[0])

    print 'Unique values are:\n' + str(UniqueValues)

    for unique in UniqueValues :
            counter = 0
            print 'First block',unique
            for row in DataCaptured :
                    print 'Second block'
                    if unique == row[0] :
                            counter = int(counter)+1
            FinalList.append(unique+','+str(counter))

    print 'Final list:\n' + str(FinalList)

Here is my data.csv a,1,1-Jan-2017 a,2,3-Jan-2017 a,4,14-Feb-2017 b,21,1-Dec-2016 b,7,28-Nov-2016 — Praveen Raj Kumar
– Praveen Raj Kumar, Commented Feb 17, 2017 at 19:34
DataCaptured is a reader object. Not an reusable list. Check documentation first. — greedy52
– greedy52, Commented Feb 17, 2017 at 19:40

PrestonH · Accepted Answer · 2017-02-17 19:39:08Z

4

It's because you've already read over the entire file after the first loop; there are no more rows in the reader's iterator at this point. Use csvfile.seek(0) after the first for loop to return to the beginning of the file, and it will work.

answered Feb 17, 2017 at 19:39

PrestonH

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Comments

Scovetta · Accepted Answer · 2017-02-17 19:50:48Z

1

You could simplify the program above a bit and only iterate through the file once:

import csv

with open('/home/user/python/data.csv') as csvfile :
    unique_values = {}

    for row in csv.reader(csvfile, delimiter=','):
        element = row[0]
        if element not in unique_values:
            unique_values[element] = 0

        unique_values[element] += 1

    for unique, count in unique_values.items():
        print('{0},{1}'.format(unique, count))

answered Feb 17, 2017 at 19:50

Scovetta

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1 Comment

wwii Over a year ago

You could also make use of collections.Counter

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