Create a structure array from a list in Numpy with string and integers

Question

I've read through the documentation but cannot work out how to create a structured array of strings and integers with numpy. A shortened version of my problem is below:

foo = [['asd', 1, 2],['bgf',2,3]]
bar = np.array(foo, dtype=['S10', 'i4','i4'])

I would then like to have bar[:,0] as an array of strings and bar[:,1]and bar[:,2] as arrays of integers.

Unfortunately this gives a TypeError: data type not understood. I've tried many other ways to get it to work but cannot find anything intuitive.

Currently I am just doing bar = np.array(foo) and then casting to integer whenever I call a value from the 2nd or 3rd column, which is far from ideal.

How can I create the structure array bar that I would like from the list of lists foo?

grc · Accepted Answer · 2014-10-24 13:02:09Z

2

Here's one way to create the structured array:

>>> foo = [('asd', 1, 2),('bgf',2,3)]
>>> bar = np.array(foo, dtype='S10,i4,i4')
>>> bar
array([('asd', 1, 2), ('bgf', 2, 3)], 
      dtype=[('f0', 'S10'), ('f1', '<i4'), ('f2', '<i4')])
>>> bar['f0']
array(['asd', 'bgf'], 
      dtype='|S10')
>>> bar['f1']
array([1, 2], dtype=int32)
>>> bar['f2']
array([2, 3], dtype=int32)

If you want a normal array, with elements rather than fields, then use dtype=object.

answered Oct 24, 2014 at 13:02

grc

23.7k5 gold badges45 silver badges63 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Irshad Bhat · Accepted Answer · 2014-10-24 12:55:21Z

1

If there is more than one datatype in an array, use dtype=object.

>>> bar = np.array(foo, dtype=object)
>>> bar[:,0]
array(['asd', 'bgf'], dtype=object)
>>> bar[:,1]
array([1, 2], dtype=object)
>>> bar[:,2]
array([2, 3], dtype=object)

answered Oct 24, 2014 at 12:55

Irshad Bhat

8,7792 gold badges31 silver badges37 bronze badges

Collectives™ on Stack Overflow

Create a structure array from a list in Numpy with string and integers

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related