BUG: Using df.where converts int to float64
Pretty straightforward bug, excuse me if this has already been adressed.

```python
print(info_df.dtypes)
snp_id            object
rs_id             object
position           int32
a0                object
a1                object
exp_freq_a1      float64
info             float32
certainty        float32
type                int8
info_type0       float32
concord_type0    float32
r2_type0         float32
dtype: object

print(info_df.where(info_df["info"]>0.5).dtypes)
snp_id            object
rs_id             object
position         float64
a0                object
a1                object
exp_freq_a1      float64
info             float32
certainty        float32
type             float64
info_type0       float32
concord_type0    float32
r2_type0         float32
dtype: object
```

From what I gather it seems to be a known behavior when working with numpy. I guess I'll find a workaround.

EDIT:
As expected, fixed with a better practice
```python
print(info.loc[lambda df : df["info"] > 0.5].dtypes)
snp_id            object
rs_id             object
position           int32
a0                object
a1                object
exp_freq_a1      float64
info             float32
certainty        float32
type                int8
info_type0       float32
concord_type0    float32
r2_type0         float32
dtype: object
```

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.0.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-62-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.19.2
nose: 1.3.7
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.25.2
numpy: 1.12.0
scipy: 0.18.1
statsmodels: 0.6.1
xarray: None
IPython: 5.1.0
sphinx: 1.5.1
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2016.10
blosc: None
bottleneck: 1.2.0
tables: 3.3.0
numexpr: 2.6.1
matplotlib: 2.0.0
openpyxl: 2.4.1
xlrd: 1.0.0
xlwt: 1.2.0
xlsxwriter: 0.9.6
lxml: 3.7.2
bs4: 4.5.3
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.1.5
pymysql: None
psycopg2: None
jinja2: 2.9.4
boto: 2.45.0
pandas_datareader: None
</details>
