Group 2D numpy array elements which have equal 1st column values

Question

I have a 2D numpy array like this

[[ 569  897]
 [ 570  898]
 [ 570  900]
 [ 571  901]
 [ 571  905]
 [ 572  906]]

I want the elements wh

Answer 1

You can use np.unique to get the separating indices and then use np.split to actually split -

np.split(a, np.unique(a[:,0], return_index=1)[1][1:],axis=0)

Alternatively, with slicing and using np.flatnonzero -

np.split(a, np.flatnonzero(a[1:,0] != a[:-1,0])+1,axis=0)

Sample run -

In [63]: a
Out[63]: 
array([[569, 897],
       [570, 898],
       [570, 900],
       [571, 901],
       [571, 905],
       [572, 906]])

In [64]: out = np.split(a, np.flatnonzero(a[1:,0] != a[:-1,0])+1,axis=0)

In [65]: out[0]
Out[65]: array([[569, 897]])

In [66]: out[1]
Out[66]: 
array([[570, 898],
       [570, 900]])

In [67]: out[2]
Out[67]: 
array([[571, 901],
       [571, 905]])

In [68]: out[3]
Out[68]: array([[572, 906]])