Assign new column in DataFrame based on if value is in a certain value range
Question:
I have two DataFrames as follows:
df_discount = pd.DataFrame(data={'Graduation' : np.arange(0,1000,100), 'Discount %' : np.arange(0,50,5)})
df_values = pd.DataFrame(data={'Sum' : [20,801,972,1061,1251]})
Now my goal is to get a new column df_values[‘New Sum’] for my df_values that applies the corresponding discount to df_values[‘Sum’] based on the value of df_discount[‘Graduation’]. If the Sum is >= the Graduation the corresponding discount is applied.
Examples: Sum 801 should get a discount of 40% resulting in 480.6, Sum 1061 gets 45% resulting in 583.55.
I know I could write a funtion with if else conditions and the returning values. However, is there a better way to do this if you have very many different conditions?
Answers:
You can use pandas.DataFrame.mask. Basically if your condition is true it replaces the value. But for that your sum column has to be inside first dataframe.
https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.mask.html
You could try if pd.merge_asof()
works for you:
df_discount = pd.DataFrame({
'Graduation': np.arange(0, 1000, 100), 'Discount %': np.arange(0, 50, 5)
})
df_values = pd.DataFrame({'Sum': [20, 100, 101, 350, 801, 972, 1061, 1251]})
df_values = (
pd.merge_asof(
df_values, df_discount,
left_on="Sum", right_on="Graduation",
direction="backward"
)
.assign(New_Sum=lambda df: df["Sum"] * (1 - df["Discount %"] / 100))
.drop(columns=["Graduation", "Discount %"])
)
Result (without the last .drop(columns=...)
to see what’s happening):
Sum Graduation Discount % New_Sum
0 20 0 0 20.00
1 100 100 5 95.00
2 101 100 5 95.95
3 350 300 15 297.50
4 801 800 40 480.60
5 972 900 45 534.60
6 1061 900 45 583.55
7 1251 900 45 688.05
pandas.cut()
is made for problems like this where you need to segment your data into bins (i.e. discount % based on value range).
First define the column, the ranges, and the corresponding bins.
# The column we need to segment
col = df_values['Sum']
# The ranges: [0, 100, 200,... ,900, np.inf] means (0,100), (100,200), ... (900,inf)
graduation = np.append(df_discount['Graduation'], np.inf)
# For each range what is the corresponding bin (i.e. discount)
discount = df_discount['Discount %']
Now call pandas.cut()
and do the discount calculation.
df_values['Discount %'] = pd.cut(col,
graduation,
labels=discount)
# Convert the string label to an int for calculation
df_values['Discount %'] = df_values['Discount %'].astype(int)
df_values['New Sum'] = df_values['Sum'] * (1-df_values['Discount %']/100)
Sum Discount % New Sum
0 20 0 20.00
1 801 40 480.60
2 972 45 534.60
3 1061 45 583.55
4 1251 45 688.05
I have two DataFrames as follows:
df_discount = pd.DataFrame(data={'Graduation' : np.arange(0,1000,100), 'Discount %' : np.arange(0,50,5)})
df_values = pd.DataFrame(data={'Sum' : [20,801,972,1061,1251]})
Now my goal is to get a new column df_values[‘New Sum’] for my df_values that applies the corresponding discount to df_values[‘Sum’] based on the value of df_discount[‘Graduation’]. If the Sum is >= the Graduation the corresponding discount is applied.
Examples: Sum 801 should get a discount of 40% resulting in 480.6, Sum 1061 gets 45% resulting in 583.55.
I know I could write a funtion with if else conditions and the returning values. However, is there a better way to do this if you have very many different conditions?
You can use pandas.DataFrame.mask. Basically if your condition is true it replaces the value. But for that your sum column has to be inside first dataframe.
https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.mask.html
You could try if pd.merge_asof()
works for you:
df_discount = pd.DataFrame({
'Graduation': np.arange(0, 1000, 100), 'Discount %': np.arange(0, 50, 5)
})
df_values = pd.DataFrame({'Sum': [20, 100, 101, 350, 801, 972, 1061, 1251]})
df_values = (
pd.merge_asof(
df_values, df_discount,
left_on="Sum", right_on="Graduation",
direction="backward"
)
.assign(New_Sum=lambda df: df["Sum"] * (1 - df["Discount %"] / 100))
.drop(columns=["Graduation", "Discount %"])
)
Result (without the last .drop(columns=...)
to see what’s happening):
Sum Graduation Discount % New_Sum
0 20 0 0 20.00
1 100 100 5 95.00
2 101 100 5 95.95
3 350 300 15 297.50
4 801 800 40 480.60
5 972 900 45 534.60
6 1061 900 45 583.55
7 1251 900 45 688.05
pandas.cut()
is made for problems like this where you need to segment your data into bins (i.e. discount % based on value range).
First define the column, the ranges, and the corresponding bins.
# The column we need to segment
col = df_values['Sum']
# The ranges: [0, 100, 200,... ,900, np.inf] means (0,100), (100,200), ... (900,inf)
graduation = np.append(df_discount['Graduation'], np.inf)
# For each range what is the corresponding bin (i.e. discount)
discount = df_discount['Discount %']
Now call pandas.cut()
and do the discount calculation.
df_values['Discount %'] = pd.cut(col,
graduation,
labels=discount)
# Convert the string label to an int for calculation
df_values['Discount %'] = df_values['Discount %'].astype(int)
df_values['New Sum'] = df_values['Sum'] * (1-df_values['Discount %']/100)
Sum Discount % New Sum
0 20 0 20.00
1 801 40 480.60
2 972 45 534.60
3 1061 45 583.55
4 1251 45 688.05