What does 1 do in X = np.array(df.drop(['label'], 1))?

[landlord1984]

X = np.array(df.drop(['label'], 1))

I understand this code is to convert a Pandas's dataframe into a numpy array without a column labelled as "label".
But what is 1 doing here?

Accoding to numpy array's definition:numpy.array(object, dtype=None, copy=True, order='K', subok=False, ndmin=0)

it seems is about datatype? I have tried to delete 1, this will produce errors. So 1 is essential here.

On the other hand, if I convert one dataframe's column to a numpy array, it works without a second argument:

y = np.array(df['label'])

Thanks,

L
[/url][url=https://docs.scipy.org/doc/numpy/reference/generated/numpy.array.html#numpy.array]