Copy a column from one dataframe to another dataframe

[deanhystad]

It doesn't make any difference how many "values" there are. The dataframe operations shown are working with series (columns). A column containint 20,000 values works exactly as one containing 4.

This part is just so I have two dataframes to work with.

df1 = pd.DataFrame({"Letters": ["A", "B", "C", "D"]})
df2 = pd.DataFrame({"Numbers": [1, 2, 3, 4]})

If you prefer they could each have 1,000,000 values.

I get an error when I do this:

import pandas as pd

df1 = pd.DataFrame({"Letters": ["A", "B", "C", "D"]})
df2 = pd.DataFrame({"Numbers": [1, 2, 3, 4, 5]})

df1["Integers"] = df2["Number"]
print(df1)

Error:
Traceback (most recent call last):
  File "...\lib\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: 'Number'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File ...test.py", line 6, in <module>
    df1["Integers"] = df2["Number"]
  File "...\lib\site-packages\pandas\core\frame.py", line 3505, in __getitem__
    indexer = self.columns.get_loc(key)
  File "...\lib\site-packages\pandas\core\indexes\base.py", line 3623, in get_loc
    raise KeyError(key) from err
KeyError: 'Number'

That looks a lot like your error. I think (am quite sure) there is no "machine_status" column in df1.