Pandas - Replace values in DataFrame based on Boollean DataFrame
I am using Pandas v0.20.2 and I have a DataFrame as shown below:
df = pd.DataFrame(dict(a=[0,1], b=[3,4], c=[6,7]),
index=['spam', 'ham'])
# a b c
# spam 0 3 6
# ham 1 4 7
And I have another DataFrame that is a mask:
mask = pd.DataFrame(dict(a=[True,False], b=[True,True]),
index=['spam', 'ham'])
# a b
# spam True True
# ham False True
And I want to set the values to df
equal 999
where it is True
at mask
.
I thought the following would work:
df[mask] = 999
But this is not the case. I am getting the error below:
ValueError Traceback (most recent call last)
<ipython-input-65-503f937859ab> in <module>()
----> 1 df[mask] = 999
/home/gbra/anaconda3/envs/outer_disk/lib/python2.7/site-packages/pandas/core/frame.pyc in __setitem__(self, key, value)
2326 self._setitem_array(key, value)
2327 elif isinstance(key, DataFrame):
-> 2328 self._setitem_frame(key, value)
2329 else:
2330 # set column
/home/gbra/anaconda3/envs/outer_disk/lib/python2.7/site-packages/pandas/core/frame.pyc in _setitem_frame(self, key, value)
2364 self._check_inplace_setting(value)
2365 self._check_setitem_copy()
-> 2366 self._where(-key, value, inplace=True)
2367
2368 def _ensure_valid_index(self, value):
/home/gbra/anaconda3/envs/outer_disk/lib/python2.7/site-packages/pandas/core/generic.pyc in _where(self, cond, other, inplace, axis, level, try_cast, raise_on_error)
5096 for dt in cond.dtypes:
5097 if not is_bool_dtype(dt):
-> 5098 raise ValueError(msg.format(dtype=dt))
5099
5100 cond = cond.astype(bool, copy=False)
ValueError: Boolean array expected for the condition, not float64
I would appreciate any help with this.
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3 answers
You can override the mask with the same shape as df and then use df.mask
:
df.mask(mask.reindex(df.index, df.columns, fill_value=False), 999)
Out:
a b c
spam 999 999 6
ham 1 999 7
Regular indexing should also work at this point:
df[mask.reindex(df.index, df.columns, fill_value=False)] = 999
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