<p>将<a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.drop.html" rel="nofollow noreferrer">^{<cd1>}</a>与<a href="http://pandas.pydata.org/pandas-docs/stable/indexing.html#boolean-indexing" rel="nofollow noreferrer">^{<cd3>}</a>筛选的<code>index</code>值一起使用:</p>
<pre><code>a = app_train.select_dtypes('object').apply(pd.Series.nunique, axis = 0)
df = app_train.drop(a.index[a > 50], axis=1)
</code></pre>
<p>另一种解决方案是为缺少的<code>columns</code>添加<a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.Series.reindex.html" rel="nofollow noreferrer">^{<cd4>}</a>,然后按<code>inverted</code>条件<code><=</code>过滤:</p>
<pre><code>a = (app_train.select_dtypes('object')
.apply(pd.Series.nunique, axis = 0)
.reindex(app_train.columns, fill_value=0))
df = app_train.loc[:, a <= 50]
</code></pre>
<p><strong>样本</strong>:</p>
<pre><code>app_train = pd.DataFrame({
'A':list('abcdef'),
'B':[4,5,4,5,5,4],
'C':[7,8,9,4,2,3],
'D':[1,3,5,7,1,0],
'E':[5,3,6,9,2,4],
'F':list('aaabbb')
})
print (app_train)
A B C D E F
0 a 4 7 1 5 a
1 b 5 8 3 3 a
2 c 4 9 5 6 a
3 d 5 4 7 9 b
4 e 5 2 1 2 b
5 f 4 3 0 4 b
a = (app_train.select_dtypes('object')
.apply(pd.Series.nunique, axis = 0)
.reindex(app_train.columns, fill_value=0))
df = app_train.loc[:, a <= 5]
print (df)
B C D E F
0 4 7 1 5 a
1 5 8 3 3 a
2 4 9 5 6 a
3 5 4 7 9 b
4 5 2 1 2 b
5 4 3 0 4 b
</code></pre>