CODEWITHSUNDEEP
python
MLhacker
MLhacker

Reputation: 1512

What's happening to values in list?

For self-practice, I'm writing a dictionary program that stores data in the following data structure: [(average,month),(average,month),....,(average,month)]. The datafile is called table.csv and can be found in the link:

http://www.cse.msu.edu/~cse231/PracticeOfComputingUsingPython/05_ListsTuples/AppleStock/

The question I have is why does the list, testList[x][0], go blank when this condition becomes false?:

if dates == UniqueDates[x]:

When x = 0, such that testList[0][0], and the condition is True, the list is [474.98, 468.22, 454.7, 455.19, 439.76, 450.99]. But, when it becomes False, that same list, testList[0][0], mysteriously becomes [ ]. Why aren't the values in the list being kept? 

f = open('table.csv','r').readlines()
col = 6

testList = []
uniqueDates = []

x = 0
for i in range(1,len(f)):
    dates = f[i].split(',')[0][:7]
    column = float(f[i].split(',')[col])
    if dates not in uniqueDates:
        uniqueDates.append(dates)
        testList.append(())
        testList[x] = [],dates
    if dates == uniqueDates[x]:
        testList[x][0].append(column)
    else:
        testList[x][0].append((mean(testList[x][0]),uniqueDates[x]))
        x += 1
        testList[x][0].append(column)

Upvotes: 3

Views: 73

Answers (1)

Dave Costa
Dave Costa

Reputation: 48121

Consider this section:

if dates not in uniqueDates:
    uniqueDates.append(dates)
    testList.append(())
    testList[x] = [],dates

The first time this executes is when processing line 7, the first time the month changes. Before executing this section, x == 0; so the last line in this block replaces the first element of testList. I think you want it to replace the new empty element that you just appended.

I suspect what you want here is to simply combine the last two lines into one:

if dates not in uniqueDates:
    uniqueDates.append(dates)
    testList.append(([],dates))

Upvotes: 2

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