Adding column to list in python

Question

I have the following list :

Training_Frame = pca.fit_transform(np_scaled_train)

with the following shape (2358,4) I want to add a fifth column, This column is saved in a pandas dataframe, for that here what I've tried without any success :

Training_Frame.append(dataframe_train.iloc[:,-1])
AttributeError: 'numpy.ndarray' object has no attribute 'append'

So I've tried the following

   saved_frame = np.append(Training_Frame,dataframe_train.iloc[:,-1])
    # This works but the result has a weird shape `(11790,)` despite :
    np.shape(dataframe_train.iloc[:,-1])  # is (2358,) so I'm expecting or hopping to get  a shape like `(2358,5)

`

So I kind of don't get what's the issue here, any Idea how could I do this ?

np.append is often misused. Learn to use np.concatenate instead. — hpaulj
– hpaulj, Commented May 29, 2017 at 21:20
Despite its name, Training_Frame is not a DataFrame; it is a numpy array. You can convert it to a DataFrame with pd.DataFrame(Training_Frame). — user2285236
– user2285236, Commented May 29, 2017 at 21:21

MaxU - stand with Ukraine · Accepted Answer · 2017-05-29 21:23:23Z

1

if Training_Frame and dataframe_train are of the same length:

Training_Frame = np.column_stack((Training_Frame, dataframe_train.iloc[:,-1].values))

Alternatively you can generate a DataFrame from NDArray (as @ayhan suggested in the comments):

Training_Frame = pd.DataFrame(Training_Frame).assign(column_name=dataframe_train.iloc[:,-1])

edited May 29, 2017 at 21:23

answered May 29, 2017 at 21:18

MaxU - stand with Ukraine

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5 Comments

Engine Over a year ago

thanks for reply, I've tried your suggestion and here's what I get : IndexError: only integers, slices (:), ellipsis (...), numpy.newaxis (None) and integer or boolean arrays are valid indices

MaxU - stand with Ukraine Over a year ago

@Engine, what is the output of print(type(Training_Frame))?

Engine Over a year ago

Engine Over a year ago

thanks a lot for your help, I still have issue understand all datatypes in python :/. I'm using the first suggestion thanks again. I can accept ur answer in 5 min

MaxU - stand with Ukraine Over a year ago

@Engine, glad i could help :-)

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