econml/utilities.py
def hstack(XS):
    """
    Stack arrays in sequence horizontally (column wise).

    This is equivalent to concatenation along the second axis


    Parameters
    ----------
    XS : sequence of ndarrays
        The arrays must have the same shape along all but the second axis.

    Returns
    -------
    ndarray or SparseArray
        The array formed by stacking the given arrays. It will be sparse if the inputs are.
    """
    # Confusingly, this needs to concatenate, not stack (stack returns an array with an extra dimension)
    return concatenate(XS, 1)

    Stack arrays in sequence horizontally (column wise).

    This is equivalent to concatenation along the second axis


    Parameters
    ----------
    XS : sequence of ndarrays
        The arrays must have the same shape along all but the second axis.

    Returns
    -------
    ndarray or SparseArray
        The array formed by stacking the given arrays. It will be sparse if the inputs are.
    
Stack arrays in sequence horizontally (column wise).
This is equivalent to concatenation along the second axis

Parameters

XS : sequence of ndarrays
The arrays must have the same shape along all but the second axis.

Returns

ndarray or SparseArray
The array formed by stacking the given arrays. It will be sparse if the inputs are.
Stack arrays in sequence horizontally ( column wise ) . This is equivalent to concatenation along the second axis Parameters XS : sequence of ndarrays The arrays must have the same shape along all but the second axis . Returns ndarray or SparseArray The array formed by stacking the given arrays . It will be sparse if the inputs are .
def hstack(XS):
    return concatenate(XS, 1)
def hstack ( XS ) : return concatenate ( XS , 1 )
Stack arrays in sequence horizontally (column wise).
Stack arrays in sequence horizontally ( column wise ) .
"""
    Stack arrays in sequence horizontally (column wise).

    This is equivalent to concatenation along the second axis


    Parameters
    ----------
    XS : sequence of ndarrays
        The arrays must have the same shape along all but the second axis.

    Returns
    -------
    ndarray or SparseArray
        The array formed by stacking the given arrays. It will be sparse if the inputs are.
    """ # Confusingly, this needs to concatenate, not stack (stack returns an array with an extra dimension)
XS