NDFrame.filter -> NDFrame.select
State: closed

- [x] closes #26642
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

This PR moves ``NDFrame.filter`` over to ``NDFrame.select`` and deprecates ``NDFrame.filter``.

I'm not completely happy with the siganture from ``.filter``, and got some discussion points in #26642. The current PR can be seen as a first version, to be changed, if there's agreement,

Labels:
name: API Design
name: Deprecate
description: Functionality to remove in pandas

Comments:
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=h1) Report
> Merging [#26866](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/430f0fd04646a0ab44ccbfbad706dfe22e9fabfe?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26866/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26866      +/-   ##
==========================================
- Coverage   91.88%   91.87%   -0.01%     
==========================================
  Files         179      179              
  Lines       50696    50700       +4     
==========================================
- Hits        46581    46580       -1     
- Misses       4115     4120       +5
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.46% <100%> (ø)` | :arrow_up: |
| #single | `41.09% <14.28%> (-0.08%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/26866/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `94.2% <100%> (+0.01%)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26866/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `88.88% <0%> (-11.12%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26866/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.88% <0%> (-0.12%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/26866/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `90.84% <0%> (-0.11%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=footer). Last update [430f0fd...192fa91](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=h1) Report
> Merging [#26866](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/430f0fd04646a0ab44ccbfbad706dfe22e9fabfe?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26866/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26866      +/-   ##
==========================================
- Coverage   91.88%   91.87%   -0.01%     
==========================================
  Files         179      179              
  Lines       50696    50700       +4     
==========================================
  Hits        46581    46581              
- Misses       4115     4119       +4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.46% <100%> (ø)` | :arrow_up: |
| #single | `41.11% <14.28%> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/26866/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `94.2% <100%> (+0.01%)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26866/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `88.88% <0%> (-11.12%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26866/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.88% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=footer). Last update [430f0fd...69c37a7](https://codecov.io/gh/pandas-dev/pandas/pull/26866?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

We need to have at least one release without NDFrame.select, before we can change it to be the new name for filter, right?
I've set up an issue at #26642. 
I'm closing this donw temporarily. As I'vr said in #26642, I'm in favor ofmaking a specialized method that wouldn't overlap too much ``.loc``.