Key Error 6 while trying to access a matrix/array - python-3.x

Question

import pandas as pd
import numpy as np
df = pd.read_csv("ia-infect-dublin.csv", header = None)
df.columns = ['Person_ID', 'Contacted']
df = df.sort_values(by=['Person_ID', 'Contacted'])
unique = df['Person_ID'].unique()
unique = np.append(unique, ["Start"])
matrix = pd.DataFrame(0, columns=unique, index=unique, dtype=int)
l_group = df.groupby('Person_ID')
for name, group in l_group:
i = 0
for index, rows in group.iterrows():
if i ==0:
matrix.loc[['Start'], rows['Person_ID']] += 1
previous_state = rows['Person_ID']
i = 1
else:
matrix.loc[previous_state, rows['Person_ID']] += 1
print(matrix.head())
I am making a transition matrix of where it goes through the csv file and find the frequency of changes from one person to another. A -> B -> C -> D and adds the total count. However, I receive an error:
Traceback (most recent call last):
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/indexes/base.py", line 3621, in get_loc
return self._engine.get_loc(casted_key)
File "pandas/_libs/index.pyx", line 136, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/index.pyx", line 163, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/hashtable_class_helper.pxi", line 5198, in pandas._libs.hashtable.PyObjectHashTable.get_item
File "pandas/_libs/hashtable_class_helper.pxi", line 5206, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 6
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/Users/vydang/Documents/FA22/BMI5007/Homeworks/hw10/testing", line 23, in <module>
matrix.loc[['Start'], rows['Person_ID']] += 1
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/indexing.py", line 961, in __getitem__
return self._getitem_tuple(key)
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/indexing.py", line 1140, in _getitem_tuple
return self._getitem_lowerdim(tup)
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/indexing.py", line 867, in _getitem_lowerdim
section = self._getitem_axis(key, axis=i)
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/indexing.py", line 1202, in _getitem_axis
return self._get_label(key, axis=axis)
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/indexing.py", line 1153, in _get_label
return self.obj.xs(label, axis=axis)
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/generic.py", line 3849, in xs
return self[key]
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/frame.py", line 3505, in __getitem__
indexer = self.columns.get_loc(key)
File "/Users/vydang/opt/anaconda3/lib/python3.9/site-packages/pandas/core/indexes/base.py", line 3623, in get_loc
raise KeyError(key) from err
KeyError: 6
I have tried to see where the error is by:
value = '6'
if value in matrix.index:
print(matrix.loc[value])
else:
print("Not in index")
And it does populate and I have also tried:
matrix['6']
matrix.loc['6']
and no error occurs. Is there any other possible reasons that this may be occuring?
I have tried to check if the index has the 'Start' and it did.