Python - trying to create a conditional column with for loop-CodePudding

I want to create a conditional column using for loop but the condition is not working.

Data:

Index   Salesman ID OrderDate   Final_Price month
0   2887    01-01-2020  57.8259 1
1   3532    04-01-2020  297.5574    1
2   2911    07-01-2020  107.3754    1
3   3276    10-01-2020  151.8066    1
4   3013    13-01-2020  82.0116 1
239 2933    18-12-2021  73.3788 12
240 3093    21-12-2021  453.5685    12
241 3460    24-12-2021  102.606 12
242 3456    27-12-2021  54.978  12
243 3665    30-12-2021  123.7104    12

I want to create a new column named "Quarter" using the following logic. I found other ways to do this but I would like to know what is wrong with this code:

for i in sales_data["month"]:
    if i >= 1 and i <= 3:
    sales_data["Quarter"] = "Q1"
 elif i >= 4 and i <= 6:
     sales_data["Quarter"] = "Q2"
 elif i >= 7 and i <= 9:
     sales_data["Quarter"] = "Q3"
 else:
     sales_data["Quarter"] = "Q4"

This code returns the following:

Salesman ID OrderDate   Final_Price     month   Quarter
2887        01-01-2020  57.8259         1       Q4
3532        04-01-2020  297.5574        1       Q4
2911        07-01-2020  107.3754        1       Q4
3276        10-01-2020  151.8066        1       Q4
3013        13-01-2020  82.0116         1       Q4
... ... ... ... ...
2933        18-12-2021  73.3788         12      Q4
3093        21-12-2021  453.5685        12      Q4
3460        24-12-2021  102.606         12      Q4
3456        27-12-2021  54.978          12      Q4
3665        30-12-2021  123.7104        12      Q4

The issue with the output is that the column "Quarter" returned "Q4" for all rows.

I found a way to correct this:

Quarter = []
for i in sales_data["month"]:
if i <= 3:
    Quarter.append("Q1")
elif i >= 4 and i <= 6:
    Quarter.append("Q2")
elif i >= 7 and i <= 9:
    Quarter.append("Q3")
else:
    Quarter.append("Q4")

sales_data["Quarter"] = Quarter

CodePudding user response：

You can generate the quarter by applying a function to the month:

df['Quarter'] = df['month'].apply(lambda m: f'Q{(m-1)//3 1}')

The function computes the quarter number as

(month - 1) // 3   1

1-3 => Q1
4-6 => Q2
7-9 => Q3
10-12 => Q4

CodePudding user response：

Using the math module, we can also do it quickly.

from math import ceil

for i in sales_data["month"]:
    quarter = ceil(i/3)
    sales_data["Quarter"] = "Q%d" % quarter

P.S - Above code is not tested. It's just pseudo code so that you can change it accordingly.