Convert NaN string to null

[Paul Blelloch]

I'm probably missing something obvious here, but I'm creating a dataframe from a duct that contains a number of 'NaN' strings for missing data. Pandas seems to be interpreting these literally as strings. How do I convert them to nulls so that I can use methods such as dropna to deal with them?

[Phillip Cloud]

One option is to use the replace method :

In [10]: import pandas as pd

In [11]: df
Out[11]:
     a  b
0  NaN  1
1    1  2
2  NaN  3
3    1  1
4  NaN  2
5    1  3

In [12]: df.dtypes
Out[12]:
a    object
b     int64
dtype: object

In [13]: newdf = df.replace('NaN', np.nan)

In [14]: newdf
Out[14]:
    a  b
0 NaN  1
1   1  2
2 NaN  3
3   1  1
4 NaN  2
5   1  3

In [15]: newdf.dtypes
Out[15]:
a    float64
b      int64
dtype: object

​

--

Best,

Phillip Cloud

On Sat, Nov 29, 2014 at 9:43 PM, Paul Blelloch <paul.b...@gmail.com> wrote:

I'm probably missing something obvious here, but I'm creating a dataframe from a duct that contains a number of 'NaN' strings for missing data. Pandas seems to be interpreting these literally as strings. How do I convert them to nulls so that I can use methods such as dropna to deal with them?

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[Paul Blelloch]

Thanks. That's exactly what I was looking for. I had been missing the np.nan.