It would be helpful if you could post the full stack trace, so that we can see which line your error occurs at. In general, the more information you can provide in a question, the better.

In this case, it looks like your full_model_pipeline may somehow become a numpy array. Since you have a one-element pipeline, you could try changing

full_model_pipeline = Pipeline(steps =[
                        ('full_pipeline',full_pipeline),
                        ('model',LinearRegression())
                    ])

full_model_pipeline.fit(X_train,y_train)

to

model = LinearRegression()
model.fit(X_train, y_train)

If you debug your program by simply printing ax, you'll quickly find out that ax is a two-dimensional array: one dimension for the rows, one for the columns.

Thus, you need two indices to index ax to retrieve the actual AxesSubplot instance, like:

ax[1,1].plot(...)

If you want to iterate through the subplots in the way you do it now, by flattening ax first:

ax = ax.flatten()

and now ax is a one dimensional array. I don't know if rows or columns are stepped through first, but if it's the wrong around, use the transpose:

ax = ax.T.flatten()

Of course, by now it makes more sense to simply create each subplot on the fly, because that already has an index, and the other two numbers are fixed:

for x < plots_tot:
     ax = plt.subplot(nrows, ncols, x+1)

Note: you have x <= plots_tot, but with x starting at 0, you'll get an IndexError next with your current code (after flattening your array). Matplotlib is (unfortunately) 1-indexed for subplots. I prefer using a 0-indexed variable (Python style), and just add +1 for the subplot index (like above).

The problem is not with Pandas. This is due to NumPy. I had a similar issue and this is what I did.

Ran python -c "import numpy as np; print(np.__file__); print(np.ndarray)". The expect output will contain the location of your installed NumPy package and <class 'numpy.ndarray'> for the second print statement. In my case, it seemed that NumPy package was located in ~/.local.

I tried reinstalling NumPy in conda, but the location was still the same. So, as per this solution, I deleted ~/.local. Then the error disappeared.

There is nothing wrong with your data, your main mistake is that you need to pay attention to the plot function used. This link tells you how to plot your data. https://matplotlib.org/tutorials/introductory/pyplot.html

However I would change the last line to something like:

import matplotlib.pyplot as plt
plt.plot(y_rus)
plt.show()

or something like:

plt.scatter(y_rus)
plt.show()

In general is a bit difficult to understand what exactly you want or the format of the data, so I hope this works. Follow the tutorial it will help you understand what you really need to continue.

if you need to flatten you can directly use flatten() on numpy.ndarray object

X = X.flatten()

Link to doc: https://numpy.org/doc/stable/reference/generated/numpy.ndarray.flatten.html