Pandas-根据Boollean DataFrame替换DataFrame中的值 [英] Pandas - Replace values in a DataFrame Based on a Boollean DataFrame

问题描述

我正在使用Pandas v0.20.2，并且具有DataFrame，如下所示:

I'm using Pandas v0.20.2 and I have DataFrame, like the following:

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

我还有另一个是掩码的DataFrame:

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

我想将df中的值设置为等于999，在mask中为True.

And I want to set the values in df equal to 999 where it is True in the mask.

我认为以下方法会起作用:

I thought that the following would work:

df[mask] = 999

但事实并非如此.我收到以下错误:

But it doesn't. I get 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

在此方面的任何帮助，我将不胜感激.

I would appreciate any help on this.

推荐答案

您可以重新索引蒙版，使其具有与df相同的形状，然后使用df.mask:

You can reindex the mask to have 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

那时，常规索引编制也应该起作用:

At that point, regular indexing should also work:

df[mask.reindex(df.index, df.columns, fill_value=False)] = 999

这篇关于Pandas-根据Boollean DataFrame替换DataFrame中的值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！