econml/utilities.py
def vstack(XS):
    """
    Stack arrays in sequence vertically (row wise).

    This is equivalent to concatenation along the first axis after
    1-D arrays of shape (N,) have been reshaped to (1,N).

    Parameters
    ----------
    XS : sequence of ndarrays
        The arrays must have the same shape along all but the first axis.
        1-D arrays must have the same length.

    Returns
    -------
    ndarray or SparseArray
        The array formed by stacking the given arrays, will be at least 2-D.   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, 0)

    Stack arrays in sequence vertically (row wise).

    This is equivalent to concatenation along the first axis after
    1-D arrays of shape (N,) have been reshaped to (1,N).

    Parameters
    ----------
    XS : sequence of ndarrays
        The arrays must have the same shape along all but the first axis.
        1-D arrays must have the same length.

    Returns
    -------
    ndarray or SparseArray
        The array formed by stacking the given arrays, will be at least 2-D.   It will be sparse if the inputs are.
    
Stack arrays in sequence vertically (row wise).
This is equivalent to concatenation along the first axis after
1-D arrays of shape (N,) have been reshaped to (1,N).

Parameters

XS : sequence of ndarrays
The arrays must have the same shape along all but the first axis.
1-D arrays must have the same length.

Returns

ndarray or SparseArray
The array formed by stacking the given arrays, will be at least 2-D.   It will be sparse if the inputs are.
Stack arrays in sequence vertically ( row wise ) . This is equivalent to concatenation along the first axis after 1 - D arrays of shape ( N ) have been reshaped to ( 1 N ) . Parameters XS : sequence of ndarrays The arrays must have the same shape along all but the first axis . 1 - D arrays must have the same length . Returns ndarray or SparseArray The array formed by stacking the given arrays will be at least 2 - D . It will be sparse if the inputs are .
def vstack(XS):
    return concatenate(XS, 0)
def vstack ( XS ) : return concatenate ( XS , 0 )
Stack arrays in sequence vertically (row wise).
Stack arrays in sequence vertically ( row wise ) .
"""
    Stack arrays in sequence vertically (row wise).

    This is equivalent to concatenation along the first axis after
    1-D arrays of shape (N,) have been reshaped to (1,N).

    Parameters
    ----------
    XS : sequence of ndarrays
        The arrays must have the same shape along all but the first axis.
        1-D arrays must have the same length.

    Returns
    -------
    ndarray or SparseArray
        The array formed by stacking the given arrays, will be at least 2-D.   It will be sparse if the inputs are.
    """ # Confusingly, this needs to concatenate, not stack (stack returns an array with an extra dimension)
XS