DOC: MultiIndex Indexing Using Slices

[cancan101]

I have the following DataFrame:

    t1  t2
    b1  b1
i1   1   1

which I can index like this:

In [139]: df["t1"]
Out[139]: 
    b1
i1   1

In [140]: df["t1","b1"]
Out[140]: 
i1    1
Name: (t1, b1), dtype: int64

In [141]: df["t1"]["b1"]
Out[141]: 
i1    1
Name: b1, dtype: int64

I would expect this to work, but ti does not:

In [142]: df[:]["b1"]
KeyError: 'b1'

as well as this (which also raises an unhelpful error message):

In [143]: df[:,"b1"]
TypeError: 

[jreback]

pls read the docs

http://pandas.pydata.org/pandas-docs/dev/indexing.html

those operations are not supported in that format (and have never been), nor will for good reason

[cancan101]

@jreback I have read those docs. Okay, Is this there any easy way to accomplish dropping a level of column name hierarchy?

Also the second exception (TypeError) is not very helpful.

[cancan101]

So far my best option is:

df.T.reset_index(level=1, drop=True).T

[jorisvandenbossche]

@cancan101 df.columns = df.columns.droplevel()

[cancan101]

1. This feature is undocumented (http://pandas.pydata.org/pandas-docs/dev/search.html?q=droplevel&check_keywords=yes&area=default#)
2. Does it make sense to have an inplace option?

[jorisvandenbossche]

And there are still some more things that are undocumented. PR?

The methods specific to MultiIndex are:

pandas.MultiIndex.droplevel
pandas.MultiIndex.equal_levels
pandas.MultiIndex.from_arrays
pandas.MultiIndex.from_tuples
pandas.MultiIndex.get_loc_level
pandas.MultiIndex.get_major_bounds
pandas.MultiIndex.has_duplicates
pandas.MultiIndex.is_lexsorted
pandas.MultiIndex.levshape
pandas.MultiIndex.lexsort_depth
pandas.MultiIndex.reorder_levels
pandas.MultiIndex.sortlevel
pandas.MultiIndex.swaplevel
pandas.MultiIndex.truncate

[jtratner]

Please don't document them right now - many of those are more internal than
external and it's possible we'll be changing or deprecating some of them in
the next release. I'd prefer not to put them in docs until we've decided
which are actually supposed to be used by end users. Definitely will be
documented in 0.14

[cancan101]

Should we create a ticket to keep track of the eventual documentation?
On Oct 20, 2013 1:11 PM, "Jeff Tratner" [email protected] wrote:

Please don't document them right now - many of those are more internal than
external and it's possible we'll be changing or deprecating some of them in
the next release. I'd prefer not to put them in docs until we've decided
which are actually supposed to be used by end users. Definitely will be
documented in 0.14

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/5280#issuecomment-26677372
.

[jreback]

related is #6301

[jreback]

this is effectively closed by #6301.

The documentation will be done when Index is refactored,