<p dir="auto">I ran into an odd behaviour when taking the intersection of two Indexes. Specifically,</p>
<div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="left = pd.Index(['A','B','A','C'])
right = pd.Index(['B','D'])
left.intersection(right)"><pre class="notranslate"><span class="pl-s1">left</span> <span class="pl-c1">=</span> <span class="pl-s1">pd</span>.<span class="pl-v">Index</span>([<span class="pl-s">'A'</span>,<span class="pl-s">'B'</span>,<span class="pl-s">'A'</span>,<span class="pl-s">'C'</span>])
<span class="pl-s1">right</span> <span class="pl-c1">=</span> <span class="pl-s1">pd</span>.<span class="pl-v">Index</span>([<span class="pl-s">'B'</span>,<span class="pl-s">'D'</span>])
<span class="pl-s1">left</span>.<span class="pl-en">intersection</span>(<span class="pl-s1">right</span>)</pre></div>
<p dir="auto">returns</p>
<div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="Index(['B', 'C'], dtype='object')"><pre class="notranslate"><span class="pl-v">Index</span>([<span class="pl-s">'B'</span>, <span class="pl-s">'C'</span>], <span class="pl-s1">dtype</span><span class="pl-c1">=</span><span class="pl-s">'object'</span>)</pre></div>
<p dir="auto">However, I would expect this to return</p>
<div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="Index(['B'], dtype='object')"><pre class="notranslate"><span class="pl-v">Index</span>([<span class="pl-s">'B'</span>], <span class="pl-s1">dtype</span><span class="pl-c1">=</span><span class="pl-s">'object'</span>)</pre></div>
<p dir="auto">If <code class="notranslate">Index(['B', 'C'], dtype='object')</code> is the intended behaviour, can someone explain the rationale behind it?</p>
<h4 dir="auto">Code Sample, a copy-pastable example if possible</h4>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="df = pd.DataFrame({'t1': pd.NaT, 't2': pd.NaT}, index=[1])
df.min(axis=1)
df.max(axis=1)
df.sum(axis=1)"><pre class="notranslate"><code class="notranslate">df = pd.DataFrame({'t1': pd.NaT, 't2': pd.NaT}, index=[1])
df.min(axis=1)
df.max(axis=1)
df.sum(axis=1)
</code></pre></div>
<h4 dir="auto">Expected Output</h4>
<p dir="auto">All results above return a <code class="notranslate">float64</code> series instead of a <code class="notranslate">datetime64[ns]</code> series.</p>
<h4 dir="auto">output of <code class="notranslate">pd.show_versions()</code></h4>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="INSTALLED VERSIONS
------------------
commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Darwin
OS-release: 15.4.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8

pandas: 0.18.0
nose: None
pip: 8.1.1
setuptools: 20.9.0
Cython: None
numpy: 1.11.0
scipy: 0.17.0
statsmodels: 0.6.1
xarray: None
IPython: 4.2.0
sphinx: None
patsy: 0.4.1
dateutil: 2.5.3
pytz: 2016.3
blosc: None
bottleneck: None
tables: None
numexpr: 2.5.2
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.4.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.12
pymysql: 0.7.2.None
psycopg2: 2.6.1 (dt dec pq3 ext lo64)
jinja2: 2.8
boto: None"><pre class="notranslate"><code class="notranslate">INSTALLED VERSIONS
------------------
commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Darwin
OS-release: 15.4.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8

pandas: 0.18.0
nose: None
pip: 8.1.1
setuptools: 20.9.0
Cython: None
numpy: 1.11.0
scipy: 0.17.0
statsmodels: 0.6.1
xarray: None
IPython: 4.2.0
sphinx: None
patsy: 0.4.1
dateutil: 2.5.3
pytz: 2016.3
blosc: None
bottleneck: None
tables: None
numexpr: 2.5.2
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.4.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.12
pymysql: 0.7.2.None
psycopg2: 2.6.1 (dt dec pq3 ext lo64)
jinja2: 2.8
boto: None
</code></pre></div>