Splitting a date string within a Nested List to group lists by the month - Python

user_15597953 0
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This is a homework assignment. I am not allowed to use libraries etc. The purpose is to learn and understand nested lists, loops and filtering by conditionals in Python.

I have a nested list of data, a short extract is below. It is 200 lines long.

patients = [ ['Milos', 'Jones', '15/01/20', 'male', 'smoker', '210'],
             ['Delia', 'Chan', '15/03/20', 'female', 'non-smoker', '170'],
             ['Denise', 'Ross', '13/02/20', 'female', 'non-smoker', '150'] ]

I need to be able to filter the list by gender and the month. Convert the [5] element in each list to an integer ready.

To filter by gender I have written this code:

female_patients = []
for solo_patient in patients:
    if solo_patient[3] == 'female':
        female_patients.append(solo_patient)

I have converted the element to an integer using :

for solo_patient in patients:
    solo_patient[5] = int(solo_patient[5])

Both work and output what I need.

However, I am trying to split the data into strings and convert to integers so I can filter by month. I used similar logic to above but I can't make it work properly.

for solo_patient in patients:
patients[2] = [solo_patient[2].split('/')

This gives me an error " IndexError: list index out of range"

If I use the code:

for solo_patient in patients:
patients = [solo_patient[2].split('/')

It splits the date into "MM", "DD", "YY" but I lose the other data.

When I do get it split, I need to convert the date strings into integers, then using a loop for range(1,13) go through and group by the month. Then I need to perform basic statistics on the data for male/female. I think I know how to do that once I have filtered the lists correctly. I would appreciate any advice, explanations or constructive feedback.

filter date nested python
2 Answers

Here is a possible solution to group patients by month:

patients_by_month = {month: [] for month in range(1, 13)}
for patient in patients:
    mm = int(patient[2].split('/')[1])
    patients_by_month[mm].append(patient)

I you run this code over your example then patients_by_month is:

{1: [['Milos', 'Jones', '15/01/20', 'male', 'smoker', '210']],
 2: [['Denise', 'Ross', '13/02/20', 'female', 'non-smoker', '150']],
 3: [['Delia', 'Chan', '15/03/20', 'female', 'non-smoker', '170']],
 4: [], 5: [], 6: [], 7: [], 8: [], 9: [], 10: [], 11: [], 12: []}

Specifically, patients_by_month is a dictionary that maps each month to a list of patients.

user_52961060

let me tell you what you're doing wrong here -

for solo_patient in patients:
    patients[2] = solo_patient[2].split('/')

here's in each for loop call i.e 0,1,2. You're trying to update the last row -> patients[2].

patients[2] = ['Denise', 'Ross', '13/02/20', 'female', 'non-smoker', '150']

patients[2] value will change if you do something like this inside for loop.

Let's do this instead -

for solo_patient in patients:
    print((solo_patient[2]).split('/'))

The above statement will give you another list -

['15', '01', '20']
['15', '03', '20']
['13', '02', '20']

Now, if you wanna assign this value back to the original list at a specific index i.e 2 of each row. you can do something like this

for index,solo_patient in enumerate(patients):
    patients[index][2] = tuple((solo_patient[2]).split('/'))
    
print(patients)

This will print -

[['Milos', 'Jones', ('15', '01', '20'), 'male', 'smoker', '210'],
 ['Delia', 'Chan', ('15', '03', '20'), 'female', 'non-smoker', '170'],
 ['Denise', 'Ross', ('13', '02', '20'), 'female', 'non-smoker', '150']]

To Extract months.

month_list= [] #initialize empty list
for solo_patient in patients:
    date = solo_patient[2].split('/') # split and create list
    month_list.append(int(date[1])) # select the value at index 1 and convert it to int and then append it to month list.
    
print(month_list)
user_154380330
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