How to add a column of strings to a numpy string matrix?

Question

I have a matrix of strings. How do I add a column to the front, like

[['a','b'],   ==>   [['e','a','b'],
 ['c','d'],          ['e','c','d'],
 ['a','b'],   ==>    ['e','a','b'],
 ['c','d'],          ['e','c','d'],
 ['a','b'],   ==>    ['e','a','b'],
 ['c','d']]          ['e','c','d']]

same as any other array: http://stackoverflow.com/questions/5064822/numpy-how-to-add-items-into-an-array/5068182#5068182 — Paul, Apr 22 '13 at 20:38

score 1 · Answer 1 · edited May 23 '17 at 12:15

The answer in @Paul's comments explains it all. Adding here for completeness.

In [1]: a = np.tile(np.array([["a","b"], ["c","d"]]), (3,1))

In [2]: a 
Out[2]: array([['a', 'b'],
       ['c', 'd'],
       ['a', 'b'],
       ['c', 'd'],
       ['a', 'b'],
       ['c', 'd']], 
      dtype='<U1')

In [3]: e = np.tile("e", a.shape[0])[None].T # REF: https://stackoverflow.com/a/11885718/155813

In [4]: e 
Out[4]: array([['e'],
       ['e'],
       ['e'],
       ['e'],
       ['e'],
       ['e']], 
      dtype='<U1')

In [5]: np.hstack([e, a]) 
Out[5]: array([['e', 'a', 'b'],
       ['e', 'c', 'd'],
       ['e', 'a', 'b'],
       ['e', 'c', 'd'],
       ['e', 'a', 'b'],
       ['e', 'c', 'd']], 
      dtype='<U1')

How to add a column of strings to a numpy string matrix?

1 Answers1