Credit Card Transaction Analysis

Note

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Description: §

You are a fintech professional working for a bank. Your team has collected a dataset of credit card transactions from various customers, including transaction dates, amounts, categories, and merchant names. However, the data is messy and needs to be cleaned and analyzed to extract valuable insights.

Task: §

Use pandas to clean and analyze the dataset, answering the following questions:

• What is the total transaction amount for each category (e.g., Food, Entertainment, Shopping)?
• Which merchant has the highest total transaction amount?
• What is the average transaction amount per day for each category?

Bonus Question: §

Identify the top 3 categories with the highest average transaction amount on weekends (Saturday and Sunday).

Answer: Travel, Entertainment, Food (in that order)

# import libraries
import pandas as pd
import numpy as np

Generate the data §

The code below generates a sample dataset with 105 rows and 4 columns (date, amount, category, and merchant). The data includes some missing values and duplicates to simulate real data in the wild.

# set the seed
np.random.seed(0)
 
# hold the values to randomly pick from
categories = ['Food', 'Entertainment', 'Shopping', 'Travel']
merchants = ['McDonalds', 'Amazon', 'Netflix', 'Expedia', 'Starbucks']
dates = pd.date_range('2024-01-01', '2024-01-31')
 
# generate the data
data = {
'date': np.random.choice(dates, size=100),
'amount': np.random.uniform(10, 100, size=100),
'category': np.random.choice(categories, size=100),
'merchant': np.random.choice(merchants, size=100)
}
 
# add the data to our dataframe
df = pd.DataFrame(data)
 
# introduce some missing values
# we randomly select 5 index values and set the column "amount" to null
df.loc[np.random.choice(df.index, size=5), 'amount'] = np.nan
 
# introduce some duplicates
# we select the first 5 rows and append them to the dataframe
dupes = df.iloc[:5]
df = pd.concat([df, dupes])
 
df.head()

	date	amount	category	merchant
0	2024-01-13	67.084665	Food	Starbucks
1	2024-01-16	96.305434	Shopping	Expedia
2	2024-01-22	68.751129	Travel	Expedia
3	2024-01-01	67.155299	Travel	Amazon
4	2024-01-04	NaN	Entertainment	Amazon

The data types of the columns look good.

Do you see the Non-Null count column and the value of 99? This is how we can determine if our data has any null values.

df.info()

<class ‘pandas.core.frame.DataFrame’> Index: 105 entries, 0 to 4 Data columns (total 4 columns):

Column Non-Null Count Dtype §

---

0 date 105 non-null datetime64[ns] 1 amount 99 non-null float64
2 category 105 non-null object
3 merchant 105 non-null object
dtypes: datetime64[ns](1), float64(1), object(2) memory usage: 4.1+ KB

Duplicates §

Let’s take care of the duplicates in the data

# here is how we can identify the duplicates
df[df.duplicated()]

	date	amount	category	merchant
0	2024-01-13	67.084665	Food	Starbucks
1	2024-01-16	96.305434	Shopping	Expedia
2	2024-01-22	68.751129	Travel	Expedia
3	2024-01-01	67.155299	Travel	Amazon
4	2024-01-04	NaN	Entertainment	Amazon

# here is how we can pinpoint one of the duplicates
df[df.loc[:,'amount'].apply(lambda x: np.isclose(x,67.084665))]

	date	amount	category	merchant
0	2024-01-13	67.084665	Food	Starbucks
0	2024-01-13	67.084665	Food	Starbucks

# pandas makes it very easy to get rid of the duplicates
df = df.drop_duplicates()
 
df.head()

	date	amount	category	merchant
0	2024-01-13	67.084665	Food	Starbucks
1	2024-01-16	96.305434	Shopping	Expedia
2	2024-01-22	68.751129	Travel	Expedia
3	2024-01-01	67.155299	Travel	Amazon
4	2024-01-04	NaN	Entertainment	Amazon

Missing Values §

Here I am just going to fill any missing values with the previous known value. If I don’t find any, I will simply get rid of the row.

# these are the null values
df[df.loc[:,'amount'].isna()]

	date	amount	category	merchant
4	2024-01-04	NaN	Entertainment	Amazon
23	2024-01-15	NaN	Food	Expedia
24	2024-01-25	NaN	Travel	McDonalds
49	2024-01-08	NaN	Entertainment	McDonalds
87	2024-01-24	NaN	Shopping	McDonalds

Let’s see if we can look at the null rows and the previous row so we can see if forward fill will work for all the rows.

As you can see from the table below, we don’t have a previous not-null value for any of our missing data. This means we cannot make a guess on what should be there and we just need to remove those rows.

# make sure data is ordered
df = df.sort_values(by=['date','category','merchant'])
 
# make sure index values are in order
# drop=True, this is to completely get rid of the old index and prevent it from being added as a column
df = df.reset_index(drop=True)
 
# get null rows
null_rows = df[df['amount'].isnull()]
 
# get null indexes
null_indices = null_rows.index
 
# get previous rows
previous_rows = df.loc[null_indices - 1]
 
# combine them
pd.concat([null_rows,previous_rows]).sort_index()

	date	amount	category	merchant
11	2024-01-03	70.789517	Food	Netflix
12	2024-01-04	NaN	Entertainment	Amazon
28	2024-01-08	18.313650	Entertainment	Amazon
29	2024-01-08	NaN	Entertainment	McDonalds
47	2024-01-14	71.979506	Travel	McDonalds
48	2024-01-15	NaN	Food	Expedia
80	2024-01-24	50.604329	Shopping	Expedia
81	2024-01-24	NaN	Shopping	McDonalds
85	2024-01-25	77.425285	Entertainment	Netflix
86	2024-01-25	NaN	Travel	McDonalds

Let’s remove the null rows under the amount column

# drop nulls
df = df.dropna()
 
# verify
df.info()

<class ‘pandas.core.frame.DataFrame’> Index: 95 entries, 0 to 99 Data columns (total 4 columns):

Column Non-Null Count Dtype §

---

0 date 95 non-null datetime64[ns] 1 amount 95 non-null float64
2 category 95 non-null object
3 merchant 95 non-null object
dtypes: datetime64[ns](1), float64(1), object(2) memory usage: 3.7+ KB

Let’s Answer The Questions §

# What is the total transaction amount for each category (e.g., Food, Entertainment, Shopping)?
group = df.groupby('category')
 
group.sum(numeric_only=True)

	amount
category
Entertainment	1576.840628
Food	1063.905275
Shopping	1060.962022
Travel	1822.804450

# Which merchant has the highest total transaction amount?
group = df.groupby('merchant')
 
group.sum(numeric_only=True).sort_values(by='amount', ascending=False).head(1)

	amount
merchant
McDonalds	1453.475029

# What is the average transaction amount per day for each category?
group = df.groupby(['date','category'])
 
# show top 7 rows
group.mean(numeric_only=True).head(7)

		amount
date	category
2024-01-01	Entertainment	29.657538
Shopping	73.336355
Travel	46.258544
2024-01-02	Entertainment	19.257702
Food	35.962879
Shopping	89.060697
Travel	89.037412

Can You Solve the Bonus Question? §

Identify the top 3 categories with the highest average transaction amount on weekends (Saturday and Sunday).