Check and add based of the first 4 digits of each element in a list in Python

Question

I've been struggling with this for the last 3 hours. I need to make a code that, using only lists:

1. Takes the input of various IDs and turns them into lists. To do that I made this code:

   def getID():
       id = input("Enter the IDs separated by a space: ")
       idlist = id.split()
       print (get2015(idlist))
       return ""
   

2. After getting the input, check from what year they are. The Ids have the following format (20(15-22)xxxxxx, for example, 2015123456, where the first four digits indicate on what year the person was born. Then, add how many people was born in that year. This is what I tried for the year 2015 but isn't working.

   def get(id):
   
       sum= 0
       for x in id[:3]:
           if x == "2015":
               sum+= 1
   return sum
   

An example of the output I need would be:

Input: 

2015000000, 2016000000, 2015000011

Output:

Born in 2015: 2
Born in 2016 : 1

How could I solve this? Thanks in advance.

Answer 1

The ideal solution would be to use a dictionary.

def getID():
    id = input("Enter the IDs separated by a space: ")
    idlist = id.split(", ") #In your input example you separate them by comma
    for id in idlist:
        addBirth(id[:4])
    
    print(birthData)

birthData = {} #Create an empty dictionary
def addBirth(year):
    #Check if key exists
    if year in birthData:
        birthData[year] += 1
    else: 
        #If the key wasn't present create a new key and initialise it to 1
        birthData[year] = 1

getID() with the input 2015000000, 2016000000, 2015000011 outputs the following:

{'2015': 2, '2016': 1}

However, because you can't use dictionaries, you can use list indices.

startYear = 2015
endYear = 2022

yearCount = endYear - startYear

#Create a list with as many items as years, all initialised to 0
birthData = [0]*yearCount 

def addBirth(year):
    birthData[int(year) - startYear] += 1

With the same input, it outputs:

[2, 1, 0, 0, 0, 0, 0] 

In order to print the data like you suggested (only for the list version):

def printBirthData(birthData):
    #For each year in the year range (2015 - 2022)
    for year in range(yearCount):
        #Only if there has been at least 1 birth that year
        if birthData[year] != 0:
            #Using f strings format the year and the year's data
            print(f"Born in {startYear + year}: {birthData[year]}")

Outputs:

Born in 2015: 2
Born in 2016: 1

Answer 2

Use Counter here:

from collections import Counter
inp = ["2015000000", "2016000000", "2015000011"]
print(Counter([x[:4] for x in inp]))  # Counter({'2015': 2, '2016': 1})

Answer 3

I'd set up a separate dictionary of years, loop over the entries in your list of IDs, and check if the first four digits in it correspond to a year in the dictionary. If yes, increase its value in the dictionary by one. If not, add it as a new key to the dictionary with value one:

years = dict()
for id in idlist:
    year = id[:4]
    if year in years.keys():
        years[year] += 1
    else:
        years[year] = 1

Answer 4

Try this : the list years will store from 2015 to 2022 count.

example: years[0] is for 2015

fun getSum(idList):
    years = [0,0,0,0,0,0,0,0]
    for id in idList :
        year = int(id[:4])
        years[year-2015] += 1
    return years

idList = ['201567899','202267868']
years = getSum(idList)
for i in range(len(years)):
    print('Born in {} : {}'.format(i+2015,years[i]))