[skip ci] wip

Author: MarcoGorelli

web/pandas/pdeps/0005-no-default-index-mode.md

@@ -8,18 +8,18 @@
 
 ## Abstract
 
-The suggestion is to add a ``NoRowIndex`` class. Internally, it would act like
-a ``RangeIndex``, but it would enable users who don't want to think about row
-labels to not need to.
+The suggestion is to add a ``NoRowIndex`` class. Internally, it would act a bit like
+a ``RangeIndex``, but some methods would be stricter. The ultimate objective would be
+to enable users who don't want to think about row labels to not need to.
 
 ## Motivation
 
 The Index can be a source of confusion and frustration for pandas users. For example, let's consider the inputs
 
 ```python
-In [37]: ser1 = pd.Series([10, 15, 20, 25], index=[1, 2, 3, 5], name='sender')
+In [37]: ser1 = pd.Series([10, 15, 20, 25], index=[1, 2, 3, 5])
 
-In [38]: ser2 = pd.Series([10, 15, 20, 25], index=[1, 2, 3, 4], name='receiver')
+In [38]: ser2 = pd.Series([10, 15, 20, 25], index=[1, 2, 3, 4])
 
 Then:
 
@@ -33,7 +33,7 @@ Then:
   3    40.0
   4     NaN
   5     NaN
-  Name: amount, dtype: float64
+  dtype: float64
   ```
 
 - concatenation, even with `ignore_index=True`, still aligns on the index (https://github.com/pandas-dev/pandas/issues/25349):
@@ -61,19 +61,20 @@ Then:
   dtype: int64
   ```
 
-With ``NoRowIndex`` DataFrames/Series, users who don't want to worry about indices wouldn't need to.
+A ``NoRowIndex`` DataFrames/Series would be a first step towards enabling users who
+don't want to worry about indices to not need to.
 
 ## Scope
 
-This proposal deals exclusively with the ``NoRowIndex``. To allow users to "opt-out" of having to think
+This proposal deals exclusively with the ``NoRowIndex`` class. To allow users to "opt-out" of having to think
 about row labels, the following could also be useful:
 - a ``pd.set_option('mode.no_default_index')`` mode which would default to creating new ``DataFrame``s and
   ``Series`` with ``NoRowIndex`` instead of ``RangeIndex``;
 - giving ``as_index`` options to methods which currently create an index
   (e.g. ``value_counts``, ``.sum()``, ``.pivot_table``) to just insert a new column instead of creating an
   ``Index``.
 
-However, neither of the above will be discussed here. Only the ``NoRowIndex`` object will be discussed here.
+However, neither of the above will be discussed here.
 
 ## Detailed Description
 
@@ -83,7 +84,7 @@ in some cases:
 - `name` could only be `None`;
 - `start` could only be `0`, `step` `1`;
 - when appending a ``NoRowIndex``, the result would still be ``NoRowIndex``;
-- when slicing, one would still get a `NoRowIndex`;
+- the ``NoRowIndex`` class would be preserved under slicing;
 - it could only be aligned with another ``Index`` if it's also ``NoRowIndex`` and if it's of the same length;
 - ``DataFrame`` columns can't be `NoRowIndex` (so ``transpose`` would need some adjustments when called on a ``NoRowIndex`` ``DataFrame``);
 - `insert` and `delete` should raise. As a consequence, if ``df`` is a ``DataFrame`` with a
@@ -124,7 +125,7 @@ In [11]: pd.concat([df, df]).index
 Out[11]: NoRowIndex(len=4)
 ```
 
-Appending anything other than another ``NoRowIndex`` would raise.
+Appending anything index other than another ``NoRowIndex`` would raise.
 
 ### Slicing a ``NoRowIndex``
 
@@ -208,7 +209,7 @@ Of the above changes, this may be the only one that would need implementing with
 ## Usage and Impact
 
 By itself, ``NoRowIndex`` would be of limited use. To become useful and user-friendly,
-a mode ``no_default_index`` could be introduced which, if introduced, would change
+a mode ``no_default_index`` could be introduced which, if enabled, would change
 the ``default_index`` function to return a ``NoRowIndex`` of the appropriate length.
 In particular, ``.reset_index()`` would result in a ``DataFrame`` with a ``NoRowIndex``.
 Likewise, a ``DataFrame`` constructed without explicitly specifying ``index=``.