[Numpy-discussion] stacking scalars with column vector

Olivier Delalleau shish at keba.be
Sun Dec 4 14:57:07 EST 2011

You can do it in one shot with:

x = np.vstack((Xstart, A[:, 0:1], Xend))

Using A[:, 0:1] instead of A[:, 0] lets you keep it as a 2d matrix (this
should answer your last question).
Then the scalars Xstart and Xend will automatically be broadcasted to
accomodate the shape of A[:, 0:1], so you don't need to write [[Xstart]]
and [[Xend]].

-=- Olivier

2011/12/4 Santhosh R <san.programming at gmail.com>

> Hi ,
> I am trying to learn python to convert some of my mlab codes to python.Am
> new to python.Some help here would be appreciated
> I am trying to make a column vector by stacking two scalars-->Xstart,Xend
> and second column of n X 2 2Darray-->A
> In matlab the code is b=[Xstart;A(:,1);Xend]
> I have made the following code
> import numpy as np
> x=np.array([[Xstart]])
> arr_temp=np.array([A[:,0]])
> x=np.vstack((x,arr_temp.T))
> x=np.vstack((x,[[Xend]]))
> This works, but is there a more elegant way of doing this.
> Also if i define arr_temp as   arr_temp=A[:,0], the array arr_temp which
> is supposed to be of shape (n,1) shows as (n,) .Why is this
> Thanks
> Santhosh
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