pandas unable to read from large StringIO object

Question

I\'m using pandas to manage a large array of 8-byte integers. These integers are included as space-delimited elements of a column in a comma-delimited CSV file, and the array si

Answer 1

There are two issues here, one fundamental and one you simply haven't come across yet. :^)

First, after you write to c, you're at the end of the (virtual) file. You need to seek back to the start. We'll use a smaller grid as an example:

>>> a = np.random.randint(0,256,(10,10)).astype('uint8')
>>> b = pd.DataFrame(a)
>>> c = StringIO()
>>> b.to_csv(c, delimiter=' ', header=False, index=False)
>>> next(c)
Traceback (most recent call last):
  File "<ipython-input-57-73b012f9653f>", line 1, in <module>
    next(c)
StopIteration

which generates the "no columns" error. If we seek first, though:

>>> c.seek(0)
>>> next(c)
'103,3,171,239,150,35,224,190,225,57\n'

But now you'll notice the second issue-- commas? I thought we requested space delimiters? But to_csv only accepts sep, not delimiter. Seems to me it should either accept it or object that it doesn't, but silently ignoring it feels like a bug. Anyway, if we use sep (or delim_whitespace=True):

>>> a = np.random.randint(0,256,(10,10)).astype('uint8')
>>> b = pd.DataFrame(a)
>>> c = StringIO()
>>> b.to_csv(c, sep=' ', header=False, index=False)
>>> c.seek(0)
>>> d = pd.read_csv(c, sep=' ', header=None, dtype='uint8')
>>> d
     0    1    2    3    4    5    6    7    8    9
0  209   65  218  242  178  213  187   63  137  145
1  161  222   50   92  157   31   49   62  218   30
2  182  255  146  249  115   91  160   53  200  252
3  192  116   87   85  164   46  192  228  104  113
4   89  137  142  188  183  199  106  128  110    1
5  208  140  116   50   66  208  116   72  158  169
6   50  221   82  235   16   31  222    9   95  111
7   88   36  204   96  186  205  210  223   22  235
8  136  221   98  191   31  174   83  208  226  150
9   62   93  168  181   26  128  116   92   68  153