如何访问python中列表列表的特定部分以与数学模块一起使用

Question

This is an assignment for school. I have a text file which contains the following abbreviated list with each entry on a single line. The first entry is the date and the second entry after the pip is the value for stock market close, there are approximately 365 entries in the file.

8/28/2018|26064.01953
8/29/2018|26124.57031
8/30/2018|25986.91992

Using the following code I have split the data into a list of lists with the date and value separated.

import os
import math
import statistics
def main ():
    infile = open('DJI.txt', 'r')
    values = infile.read()
    infile.close()
    values=values.split("\n")
    values=[value.split("|") for value in values]
    print(values)
    avg = sum([float(l[1]) for l in values])/len(values)
main()  

This gives the following output

[['8/28/2018', '26064.01953'], ['8/29/2018', '26124.57031'], ['8/30/2018', '25986.91992'],

the Avg line gives the following error: IndexError: list index out of range

My task is to create a program which calculates Average close value for the entire year. Average close value per month Highest close value and the date in which that happened. Lowest close value and the date of which that happened. Sort prices lowest to highest and write the sorted list to a new text file called DJI_Sorted.

I am have trouble with how to access the second value in the list of lists to perform the statistics on the file. I am also unsure how I would write a code which sorts the list from lowest to highest as well as the average close for each month, rather than on the entire file.

Your help is greatly appreciated.

Answer 1

You can access each list in your list with values[i] and each element of such a list with values[i][j] . So the value of the 10th date would be values[9][1] . Since you know the number of elements per inner list and it is rather small, you could also unpack your lists.

Example with three elements per inner list: a,b,c = values[i] .

You want to iterate over the entire list, so a for-loop is what you need and instead of handling indices you can directly unpack the inner lists in variables with meaningful names.

for date, value in values:
   value = float(value)
   if value > highest:
       highest = value
       highest_date = date

Another option would be a list comprehension:

avg = sum([float(l[1]) for l in values])/len(values)

Since this is your homework, I don't want to give you a complete solution, but this should be enough to solve all your questions described above. One last tip: for monthly statistics you need to further split the date, then there are multiple options to go from there (saving it the values for each month in one list/dictionary, or computing the on the fly)