Dropna argument is now respected when false in pivot_table
- [x] closes #22159
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25738?src=pr&el=h1) Report
> Merging [#25738](https://codecov.io/gh/pandas-dev/pandas/pull/25738?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9eec9b86ddba46075b63aa776f6284188de4f1ce?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25738/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25738?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25738      +/-   ##
==========================================
- Coverage   91.25%   91.24%   -0.01%     
==========================================
  Files         172      172              
  Lines       52973    52973              
==========================================
- Hits        48338    48337       -1     
- Misses       4635     4636       +1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.82% <ø> (ø)` | :arrow_up: |
| #single | `41.75% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25738?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/pivot.py](https://codecov.io/gh/pandas-dev/pandas/pull/25738/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9waXZvdC5weQ==) | `96.55% <ø> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25738/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `88.98% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25738?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/25738?src=pr&el=footer). Last update [9eec9b8...1e9ec27](https://codecov.io/gh/pandas-dev/pandas/pull/25738?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/25738?src=pr&el=h1) Report
> Merging [#25738](https://codecov.io/gh/pandas-dev/pandas/pull/25738?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/90a85e0b154833577a4023f643d8aace0c0ae7f5?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25738/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25738?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25738      +/-   ##
==========================================
- Coverage   91.89%   91.89%   -0.01%     
==========================================
  Files         175      175              
  Lines       52509    52509              
==========================================
- Hits        48255    48252       -3     
- Misses       4254     4257       +3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.45% <ø> (ø)` | :arrow_up: |
| #single | `40.74% <ø> (-0.15%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25738?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/pivot.py](https://codecov.io/gh/pandas-dev/pandas/pull/25738/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9waXZvdC5weQ==) | `96.54% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/25738/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `75% <0%> (-12.5%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/25738/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.79% <0%> (-0.12%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25738/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `90.72% <0%> (+0.1%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25738?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/25738?src=pr&el=footer). Last update [90a85e0...dab0395](https://codecov.io/gh/pandas-dev/pandas/pull/25738?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @alexander-ponomaroff! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-04-12 17:46:52 UTC > Can we clarify the meaning of `dropna`? From the docstring:
> 
> ```
>         dropna : boolean, default True
>             Do not include columns whose entries are all NaN
> ```
> It's not clear (to me) what "columns" is referring to. Input columns? Columns after some internal reshaping? Columns at the very end?

The resulting pivot table will not contain any columns with NaN values if the dropna argument is True. I believe would be the answer. I can look into it in more detail if this answer doesn't clarify it or is not specific enough. @jreback @TomAugspurger Do you have any other requests and/or feedback for this PR? can you merge master and update @jreback @WillAyd Fixed requested changes, all green now. thanks @alexander-ponomaroff 