pythonpython-3.xpandasdataframepandas-merge

AssertionError when use df.loc in python


I created a script to load data, check NA values, and fill all NA values. Here is my code:

import pandas as pd

def filter_df(merged_df, var_list):
    ind = merged_df.Name.isin(var_list)
    return merged_df[ind]

def pivot_df(df):
    return df.pivot(index='Date', columns='Name', values=['Open', 'High', 'Low', 'Close'])

def validation_df(input, summary = False):
    df = input.copy()
    # na check
    missing = df.isna().sum().sort_values(ascending=False)
    percent_missing = ((missing / df.isnull().count()) * 100).sort_values(ascending=False)
    missing_df = pd.concat([missing, percent_missing], axis=1, keys=['Total', 'Percent'], sort=False)

    # fill na
    columns = list(missing_df[missing_df['Total'] >= 1].reset_index()['index'])

    for col in columns:
        null_index = df.index[df[col].isnull() == True].tolist()
        null_index.sort()
        for ind in null_index:
            if ind > 0:
                print(df.loc[ind, col])
                print(df.loc[ind - 1, col])
                df.loc[ind, col] = df.loc[ind - 1, col]
            if ind == 0:
                df.loc[ind, col] = 0

    # outliers check
    count = []
    for col in df.columns:
        count.append(sum(df[col] > df[col].mean() + 2 * df[col].std()) + sum(df[col] < df[col].mean() - 2 * df[col].std()))
    outliers_df = pd.DataFrame({'Columns': df.columns, 'Count': count}).sort_values(by = 'Count')

    if summary == True:
        print('missing value check:/n')
        print(missing_df)
        print('/n outliers check:/n')
        print(outliers_df)

    return df

def join_df(price_df, transaction_df, var_list):

    price_df = filter_df(price_df, var_list)
    price_df = pivot_df(price_df)

    joined_df = transaction_df.merge(price_df, how = 'left', on = 'Date')
    #joined_df = validation_df(joined_df)

    return joined_df

token_path = 'https://raw.githubusercontent.com/Carloszone/Cryptocurrency_Research_project/main/datasets/1_token_df.csv'
transaction_path = 'https://raw.githubusercontent.com/Carloszone/Cryptocurrency_Research_project/main/datasets/transaction_df.csv'

var_list = ['Bitcoin', 'Ethereum', 'Golem', 'Solana']

token_df = pd.read_csv(token_path)
transaction_df = pd.read_csv(transaction_path)

df = join_df(token_df, transaction_df, var_list)
df = validation_df(df)

But it did not work. I checked my code and found this issue came from the loc(). For example:

df = join_df(token_df, transaction_df, var_list)

print(df[df.columns[15]])
print(df.loc[1,df.columns[15]])

what I got is:

0      NaN
1      NaN
2      NaN
3      NaN
4      NaN
        ..
2250   NaN
2251   NaN
2252   NaN
2253   NaN
2254   NaN
Name: (High, Solana), Length: 2255, dtype: float64

AssertionError                            Traceback (most recent call last)
<ipython-input-19-75f01cc22c9c> in <module>()
      2 
      3 print(df[df.columns[15]])
----> 4 print(df.loc[1,df.columns[15]])

2 frames
/usr/local/lib/python3.7/dist-packages/pandas/core/indexing.py in __getitem__(self, key)
    923                 with suppress(KeyError, IndexError):
    924                     return self.obj._get_value(*key, takeable=self._takeable)
--> 925             return self._getitem_tuple(key)
    926         else:
    927             # we by definition only have the 0th axis

/usr/local/lib/python3.7/dist-packages/pandas/core/indexing.py in _getitem_tuple(self, tup)
   1107             return self._multi_take(tup)
   1108 
-> 1109         return self._getitem_tuple_same_dim(tup)
   1110 
   1111     def _get_label(self, label, axis: int):

/usr/local/lib/python3.7/dist-packages/pandas/core/indexing.py in _getitem_tuple_same_dim(self, tup)
    807             # We should never have retval.ndim < self.ndim, as that should
    808             #  be handled by the _getitem_lowerdim call above.
--> 809             assert retval.ndim == self.ndim
    810 
    811         return retval

AssertionError: 

I don't know why df[column_name] is available, but df.loc[index,columns_name] is wrong.

You can check my code on Colab: https://colab.research.google.com/drive/1Yg280JRwFayW1tdp4OJqTO5-X3dGsItB?usp=sharing


Solution

  • The issue is that you're merging two DataFrames on a column they don't share in common (because you pivoted price_df, Date column became the index). Also the Date columns don't have a uniform format, so you have to make them the same. Replace your join_df function with the one below and it will work as expected.

    I added comments on the lines that had to be added.

    def join_df(price_df, transaction_df, var_list):
    
        price_df = filter_df(price_df, var_list)
        price_df = pivot_df(price_df)
    
        # After pivot the Date column is the index, and price_df has MultiIndex columns
        # since we want to merge it with transaction_df, we need to first flatten the columns
        price_df.columns = price_df.columns.map('.'.join)
    
        # and reset_index so that we have the index as the Date column
        price_df = price_df.reset_index()
    
        # the Dates are formatted differently across the two DataFrames; 
        # one has the following format: '2016-01-01' and the other '2016/1/1'
        # to have a uniform format, we convert the both Date columns to datetime objects
        price_df['Date'] = pd.to_datetime(price_df['Date'])
        transaction_df['Date'] = pd.to_datetime(transaction_df['Date'])
    
        joined_df = transaction_df.merge(price_df, how = 'left', on = 'Date')
        #joined_df = validation_df(joined_df)
    
        return joined_df
    

    Output:

               Date  total_transaction_count        Volume  gas_consumption  \
    0    2016-01-01                     2665           NaN              NaN   
    1    2016-01-02                     4217           NaN              NaN   
    2    2016-01-03                     4396           NaN              NaN   
    3    2016-01-04                     4776           NaN              NaN   
    4    2016-01-05                    26649           NaN              NaN   
    ...         ...                      ...           ...              ...   
    2250 2022-02-28                  1980533  1.968686e+06     8.626201e+11   
    2251 2022-03-01                  2013145  2.194055e+06     1.112079e+12   
    2252 2022-03-02                  1987934  2.473327e+06     1.167615e+12   
    2253 2022-03-03                  1973190  3.093248e+06     1.260826e+12   
    2254 2022-03-04                  1861286  4.446204e+06     1.045814e+12   
    
          old_ave_gas_fee  new_avg_gas_fee  new_avg_base_fee  \
    0        0.000000e+00     0.000000e+00      0.000000e+00   
    1        0.000000e+00     0.000000e+00      0.000000e+00   
    2        0.000000e+00     0.000000e+00      0.000000e+00   
    3        0.000000e+00     0.000000e+00      0.000000e+00   
    4        0.000000e+00     0.000000e+00      0.000000e+00   
    ...               ...              ...               ...   
    2250     6.356288e-08     6.356288e-08      5.941877e-08   
    2251     5.368574e-08     5.368574e-08      4.982823e-08   
    2252     5.567472e-08     5.567472e-08      4.782055e-08   
    2253     4.763823e-08     4.763823e-08      4.140883e-08   
    2254     4.566440e-08     4.566440e-08      3.547666e-08   
    
          new_avg_priority_fee  Open.Bitcoin  Open.Ethereum  ...  High.Golem  \
    0             0.000000e+00         430.0            NaN  ...         NaN   
    1             0.000000e+00         434.0            NaN  ...         NaN   
    2             0.000000e+00         433.7            NaN  ...         NaN   
    3             0.000000e+00         430.7            NaN  ...         NaN   
    4             0.000000e+00         433.3            NaN  ...         NaN   
    ...                    ...           ...            ...  ...         ...   
    2250          4.144109e-09       37707.2        2616.34  ...     0.48904   
    2251          3.857517e-09       43187.2        2922.44  ...     0.48222   
    2252          7.854179e-09       44420.3        2975.80  ...     0.47550   
    2253          6.229401e-09           NaN            NaN  ...         NaN   
    2254          1.018774e-08           NaN            NaN  ...         NaN   
    
          High.Solana  Low.Bitcoin  Low.Ethereum  Low.Golem  Low.Solana  \
    0             NaN        425.9           NaN        NaN         NaN   
    1             NaN        430.7           NaN        NaN         NaN   
    2             NaN        423.1           NaN        NaN         NaN   
    3             NaN        428.6           NaN        NaN         NaN   
    4             NaN        428.9           NaN        NaN         NaN   
    ...           ...          ...           ...        ...         ...   
    2250          NaN      37458.9       2574.12    0.41179         NaN   
    2251          NaN      42876.6       2858.54    0.45093         NaN   
    2252          NaN      43361.3       2914.70    0.43135         NaN   
    2253          NaN          NaN           NaN        NaN         NaN   
    2254          NaN          NaN           NaN        NaN         NaN   
    
          Close.Bitcoin  Close.Ethereum  Close.Golem  Close.Solana  
    0             434.0             NaN          NaN           NaN  
    1             433.7             NaN          NaN           NaN  
    2             430.7             NaN          NaN           NaN  
    3             433.3             NaN          NaN           NaN  
    4             431.2             NaN          NaN           NaN  
    ...             ...             ...          ...           ...  
    2250        43188.2         2922.50      0.47748           NaN  
    2251        44420.3         2975.81      0.47447           NaN  
    2252        43853.2         2952.47      0.43964           NaN  
    2253            NaN             NaN          NaN           NaN  
    2254            NaN             NaN          NaN           NaN  
    
    [2255 rows x 24 columns]