Pandas KeyError, accessing column

Question

I am trying to run this code: (this will download the MNIST dataset to %HOME directory!)

from sklearn.datasets import fetch_openml
mnist = fetch_openml('mnist_784', version=1)
mnist.keys()
X, y = mnist["data"], mnist["target"]

import matplotlib as mpl
import matplotlib.pyplot as plt
some_digit = X[0] # **ERROR LINE** <---------
some_digit_image = some_digit.reshape(28, 28)
plt.imshow(some_digit_image, cmap = mpl.cm.binary, interpolation="nearest")
plt.axis("off")
plt.show()

I have this error:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
~/.local/lib/python3.8/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   3079             try:
-> 3080                 return self._engine.get_loc(casted_key)
   3081             except KeyError as err:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.PyObjectHashTable.get_item()

KeyError: 0

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

KeyError                                  Traceback (most recent call last)
<ipython-input-45-d5d685fca2de> in <module>
      2 import matplotlib.pyplot as plt
      3 import numpy as np
----> 4 some_digit = X[0]
      5 some_digit_image = some_digit.reshape(28, 28)
      6 plt.imshow(some_digit_image, cmap = mpl.cm.binary, interpolation="nearest")

~/.local/lib/python3.8/site-packages/pandas/core/frame.py in __getitem__(self, key)
   3022             if self.columns.nlevels > 1:
   3023                 return self._getitem_multilevel(key)
-> 3024             indexer = self.columns.get_loc(key)
   3025             if is_integer(indexer):
   3026                 indexer = [indexer]

~/.local/lib/python3.8/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   3080                 return self._engine.get_loc(casted_key)
   3081             except KeyError as err:
-> 3082                 raise KeyError(key) from err
   3083 
   3084         if tolerance is not None:

KeyError: 0

Code example is from this book: Hands-on Machine Learning with Scikit-Learn, Keras, and TensorFlow

I tried X.iloc[0] but its also not working.

You are trying to access a column named 0. Try printing out X.columns to get an idea of what columns are available, and X.index to see what rows are available - and if you want to access a particular row + column , use - X.loc[row, col] — Mortz
– Mortz, Commented May 1, 2021 at 19:34

Ynjxsjmh · Accepted Answer · 2021-05-02 04:15:37Z

1

From your dataframe pic, there is no column header named 0. If you want to access column by index, you can use .iloc which is primarily integer position based:

df.iloc[:, 0]

Or access by column header list

df[df.columns[0]]

answered May 2, 2021 at 4:15

Ynjxsjmh

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2 Comments

MUST_DIE Over a year ago

Thx it works with df.iloc[0, :], my mistake was, that I confused column with row, actually I had to access the first row.

Ynjxsjmh Over a year ago

@Dmitry Then use df.iloc[0].

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