BUG: fix nested dict replace

[cpcloud]

closes #6342

[jreback]

see u r hacking the biggest hack in internals, putmask
because of the dtype changes that are possible

[cpcloud]

yes this is definitely a hack. np.putmask will cycle values after a false is found if the size of the array and replacement values are not equal but it will only use the next value in the replacements if the Trues are contiguous ... highly counterintuitive behavior for that if u ask me ... is there a more optimal way that i'm overlooking?

[cpcloud]

internals is kind of fun .... always have to clear out my weekend when a bug involves internals.py 😄

[cpcloud]

fyi copyto raises in the case that the sizes are unequal, but only available in numpy >= 1.7

[jreback]

I avoided copyto for that reason

yeh...putmask has a lot of 'special' cases....which I think really are just weird things numpy does

[cpcloud]

replace is turning into a god function ... worth opening an issue?

[jreback]

what do you mean?

[cpcloud]

It's just really, really large ...

[jreback]

hahah so true!

next project...you can effectively replace update with replace!

[cpcloud]

@jreback What do u think about this? I'll run a vbench to make sure this doesn't cause a hit.

[jreback]

sure....looks fine otherwise.....not even sure how often that path is actually hit (can you put a case that hits it up?)

[cpcloud]

Nested dicts hit it if they contain keys that aren't in the frame/series

df = DataFrame({'col': range(1, 5)})
df.replace({'col': {-1: 'a', 1: 'b', 2: 'c'}})

[jreback]

ok...then prob ok....not hit a lot...but do a perf check anyhow

[cpcloud]

Perf looks good:

packers_write_pack                           |   0.9952 |   0.9129 |   1.0901 |
stats_rank_average                           |  23.8746 |  21.2846 |   1.1217 |
timeseries_asof                              |   7.9971 |   7.0529 |   1.1339 |
join_dataframe_index_single_key_small        |   6.4060 |   5.5654 |   1.1510 |
timeseries_asof_nan                          |   8.0025 |   6.8281 |   1.1720 |
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------

[cpcloud]

Random network failure unrelated to this

https://travis-ci.org/cpcloud/pandas/jobs/18993144

merging