public/subjects/ai/pandas/audit/README.md

Exercise 0: Environment and libraries

The exercise is validated if all questions of the exercise are validated.

Activate the virtual environment. If you used conda run conda activate your_env

Run python --version.

Does it print Python 3.x? x >= 8

Do import jupyter, import numpy and import pandas run without any error?

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Exercise 1: Your first DataFrame

The exercise is validated if all questions of the exercise are validated.

Is the solution of question 1 the same as the "model" DataFrame? Check that the index is not 1,2,3,4,5.

For question 2, are the columns' types as below and are the types of the first value of the columns as below?

    <class 'pandas.core.series.Series'>
    <class 'pandas.core.series.Series'>
    <class 'pandas.core.series.Series'>

        <class 'str'>
        <class 'list'>
        <class 'float'>

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Exercise 2: Electric power consumption

The exercise is validated if all questions of the exercise are validated

For the solution of question 1 is drop used with axis=1.inplace=True? It may be useful to avoid to affect the result to a variable. A solution that could be accepted too (even if it's not a solution I recommend) is del.

For question 2 does the DataFrame return the output below? If the type of the index is not dtype='datetime64[ns]' the solution is not accepted. I recommend to use set_index with inplace=True to do so.

        Input: df.head().index

        Output:

        DatetimeIndex(['2006-12-16', '2006-12-16','2006-12-16', '2006-12-16','2006-12-16'],
        dtype='datetime64[ns]', name='Date', freq=None)

For question 3, are all the types float64 as below? The preferred solution is pd.to_numeric with coerce=True.

        Input: df.dtypes

        Output:

            Global_active_power      float64
            Global_reactive_power    float64
            Voltage                  float64
            Global_intensity         float64
            Sub_metering_1           float64
            dtype: object

For question 4, is df.describe() being used?

For question 5 is dropna being used and is the number of missing values equal to 0? It is important to notice that 25979 rows contain missing values (for a total of 129895). df.isna().sum() allows to check the number of missing values and df.dropna() with inplace=True allows to remove the rows with missing values.

For question 6, were one of the two approaches below used?

        #solution 1
        df.loc[:,'A'] = (df['A'] + 1) * 0.06

        #solution 2
        df.loc[:,'A'] = df.loc[:,'A'].apply(lambda x: (x+1)*0.06)

You may wonder `df.loc[:,'A']` is required and if `df['A'] = ...` works too. **The answer is no**. This is important in Pandas. Depending on the version of Pandas, it may return a warning. The reason is that you are affecting a value to a **copy** of the DataFrame and not in the DataFrame.
More details: https://stackoverflow.com/questions/20625582/how-to-deal-with-settingwithcopywarning-in-pandas

For question 7, is the output of print(filtered_df.head().to_markdown()) as below and is the number of rows equal to 449667?

| Date                |   Global_active_power |   Global_reactive_power |
|:--------------------|----------------------:|------------------------:|
| 2008-12-27 00:00:00 |                 0.996 |                   0.066 |
| 2008-12-27 00:00:00 |                 1.076 |                   0.162 |
| 2008-12-27 00:00:00 |                 1.064 |                   0.172 |
| 2008-12-27 00:00:00 |                 1.07  |                   0.174 |
| 2008-12-27 00:00:00 |                 0.804 |                   0.184 |

For question 8, is the output the following?

        Global_active_power        0.254
        Global_reactive_power      0.000
        Voltage                  238.350
        Global_intensity           1.200
        Sub_metering_1             0.000
        Name: 2007-02-16 00:00:00, dtype: float64

For question 9, is the output Timestamp('2009-02-22 00:00:00')?

For question 10 is the output of print(sorted_df.tail().to_markdown()) the following?

| Date                |   Global_active_power |   Global_reactive_power |   Voltage |
|:--------------------|----------------------:|------------------------:|----------:|
| 2008-08-28 00:00:00 |                 0.076 |                       0 |    234.88 |
| 2008-08-28 00:00:00 |                 0.076 |                       0 |    235.18 |
| 2008-08-28 00:00:00 |                 0.076 |                       0 |    235.4  |
| 2008-08-28 00:00:00 |                 0.076 |                       0 |    235.64 |
| 2008-12-08 00:00:00 |                 0.076 |                       0 |    236.5  |

For question 11, is the output the following? The solution is based on groupby which creates groups based on the index Date and aggregates the groups using the mean.

    Date
    2006-12-16    3.053475
    2006-12-17    2.354486
    2006-12-18    1.530435
    2006-12-19    1.157079
    2006-12-20    1.545658
                    ...
    2010-12-07    0.770538
    2010-12-08    0.367846
    2010-12-09    1.119508
    2010-12-10    1.097008
    2010-12-11    1.275571
    Name: Global_active_power, Length: 1433, dtype: float64

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Exercise 3: E-commerce purchases

The exercise is validated if all questions of the exercise are validated.

To validate this exercise all answers should return the expected numerical value given in the correction AND use Pandas. For example using NumPy to compute the mean doesn't respect the philosophy of the exercise which is to use Pandas.

For question 1, does the solution contain 10000 entries and 14 columns? There many solutions based on: shape, info, describe.

For question 2, is the answer 50.34730200000025?

Even if `np.mean` gives the solution, `df['Purchase Price'].mean()` is preferred

For question 3, are the min 0and the max 99.989999999999995?

For question 4, is the answer 1098?

For question 5, is the answer 30?

For question 6, are there 4932 people that made the purchase during the AM and 5068 people that made the purchase during PM? There are many ways to get the solution but the goal of this question was to make you use value_counts.

For question 7, is the answer as below? There are many ways to the solution but the goal of this question was to use value_counts.

Interior and spatial designer    31

Lawyer                           30

Social researcher                28

Purchasing manager               27

Designer, jewellery              27

For question 8, is the purchase price 75.1?

For question 9, is the email address bondellen@williams-garza.com?

For question 10, is the answer 39? The preferred solution is based on this: df[(df['A'] == X) & (df['B'] > Y)].

For question 11, is the answer 1033? The preferred solution is based on the usage of apply on a lambda function that slices the string that contains the expiration date.

For question 12, is the answer as below? The preferred solution is based on the usage of apply on a lambda function that slices the string that contains the email. The lambda function uses split to split the string on @. Finally, value_counts is used to count the occurrences.

- hotmail.com     1638
- yahoo.com       1616
- gmail.com       1605
- smith.com         42
- williams.com      37

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Exercise 4: Handling missing values

The exercise is validated if all questions of the exercise are validated (except the bonus question)

For question 1, are the two steps implemented in that order? First, convert the numerical columns to float and then fill the missing values. The first step may involve pd.to_numeric(df.loc[:,col], errors='coerce'). The second step is validated if you eliminated all missing values. However there are many possibilities to fill the missing values. Here is one of them:

example:

    df.fillna({0:df.sepal_length.mean(),
    2:df.sepal_width.median(),
    3:0,
    4:0})

For question 2, is the solution df.loc[:,col].fillna(df[col].median())?

+The solution of bonus question is accepted if you find out this answer: Once we filled the missing values as suggested in the first question, df.describe() returns this interesting summary. We notice that the mean is way higher than the median. It means that there are maybe some outliers in the data. The quantile 75 and the max confirm that: 75% of the flowers have a sepal length smaller than 6.4 cm, but the max is 6900 cm. If you check on the internet you realise this small flower can't be that big. The outliers have a major impact on the mean which equals to 56.9. Filling this value for the missing value is not correct since it doesn't correspond to the real size of this flower. That is why in that case the best strategy to fill the missing values is the median. The truth is that I modified the data set ! But real data sets ALWAYS contains outliers. Always think about the meaning of the data transformation! If you fill the missing values by zero, it means that you consider that the length or width of some flowers may be 0. It doesn't make sense.

	sepal_length	sepal_width	petal_length	petal_width
count	146	141	120	147
mean	56.9075	52.6255	15.5292	12.0265
std	572.222	417.127	127.46	131.873
min	-4.4	-3.6	-4.8	-2.5
25%	5.1	2.8	2.725	0.3
50%	5.75	3	4.5	1.3
75%	6.4	3.3	5.1	1.8
max	6900	3809	1400	1600

+Has the presence of negative values and huge values been detected? A good data scientist always check abnormal values in the dataset. YOU SHOULD ALWAYS TRY TO UNDERSTAND YOUR DATA. Print the row with index 122 ;-) This week, we will have the opportunity to focus on the data pre-processing to understand how the outliers can be handled.