Specifying dtype float32 with pandas.read_csv on pandas 0.10.1

Question

I\'m attempting to read a simple space-separated file with pandas read_csv method. However, pandas doesn\'t seem to be obeying my dtype argument.

Answer 1

0.10.1 doesn't really support float32 very much

see this http://pandas.pydata.org/pandas-docs/dev/whatsnew.html#dtype-specification

you can do this in 0.11 like this:

# dont' use dtype converters explicity for the columns you care about
# they will be converted to float64 if possible, or object if they cannot
df = pd.read_csv('test.csv'.....)

#### this is optional and related to the issue you posted ####
# force anything that is not a numeric to nan
# columns are the list of columns that you are interesetd in
df[columns] = df[columns].convert_objects(convert_numeric=True)


    # astype
    df[columns] = df[columns].astype('float32')

see http://pandas.pydata.org/pandas-docs/dev/basics.html#object-conversion

Its not as efficient as doing it directly in read_csv (but that requires
 some low-level changes)

I have confirmed that with 0.11-dev, this DOES work (on 32-bit and 64-bit, results are the same)

In [5]: x = pd.read_csv(StringIO.StringIO(data), dtype={'a': np.float32}, delim_whitespace=True)

In [6]: x
Out[6]: 
         a        b
0  0.76398  0.81394
1  0.32136  0.91063

In [7]: x.dtypes
Out[7]: 
a    float32
b    float64
dtype: object

In [8]: pd.__version__
Out[8]: '0.11.0.dev-385ff82'

In [9]: quit()
vagrant@precise32:~/pandas$ uname -a
Linux precise32 3.2.0-23-generic-pae #36-Ubuntu SMP Tue Apr 10 22:19:09 UTC 2012 i686 i686 i386 GNU/Linux

Answer 2

In [22]: df.a.dtype = pd.np.float32

In [23]: df.a.dtype
Out[23]: dtype('float32')

the above works fine for me under pandas 0.10.1