BUG: Index dtype may not be applied properly

[sinhrks]

Fixed 2 problems:

• Specified dtype is not applied to other iterables.

import numpy as np
import pandas as pd

pd.Index([1, 2, 3], dtype=int)
# Index([1, 2, 3], dtype='object')

• Specifying category to ndarray-like results in TypeError

pd.Index(np.array([1, 2, 3]), dtype='category')
# TypeError: data type "category" not understood

[jreback]

pls run perf check on this -

[jreback]

@sinhrks can you see if this affects perf?

[jreback]

I would leave all of the imports where they were, no reason to actually import them until they are used (see below)

[jreback]

actually on 2nd thought this is fine

[sinhrks]

Following is a asv result. Will consider a better path.

    before     after       ratio
  [789e07d9] [ce89f9d1]
    33.94μs    44.57μs      1.31  ctors.index_from_series_ctor.time_index_from_series_ctor
   121.86μs   173.21μs      1.42  frame_methods.frame_get_dtype_counts.time_frame_get_dtype_co
    16.45μs    27.07μs      1.65  index_object.index_float64_construct.time_index_float64_construct

[jreback]

this is prob just from the imports (e.g. a Float64Index) doesn't care about Datetimeindex, so the import adds the extra time (or the check for the import anyhow)

[sinhrks]

@jreback Thanks, suggested changes improve perf a little. I assume other slowness is caused by categorical condition moved to the top.

All benchmarks:

    before     after       ratio
  [4d4a2e33] [c3eaeb07]
    33.85μs    41.24μs      1.22  ctors.index_from_series_ctor.time_index_from_series_ctor
   129.48μs   160.86μs      1.24  frame_methods.frame_get_dtype_counts.time_frame_get_dtype_counts
    16.36μs    22.88μs      1.40  index_object.index_float64_construct.time_index_float64_construct

[jreback]

master (this is index_object.index_float64_construct.time_index_float64_construct) benchmark

In [1]: arr = np.arange(1000000.0)
In [2]: %timeit Index(arr)
The slowest run took 12.23 times longer than the fastest. This could mean that an intermediate result is being cached 
100000 loops, best of 3: 15.7 µs per loop

this branch

In [2]: %timeit Index(arr)
The slowest run took 7.49 times longer than the fastest. This could mean that an intermediate result is being cached 
10000 loops, best of 3: 19.8 µs per loop

fix jreback/pandas@29c0325

In [2]: %timeit Index(arr)
The slowest run took 11.74 times longer than the fastest. This could mean that an intermediate result is being cached 
100000 loops, best of 3: 13.8 µs per loop

will merge in a bit, thanks @sinhrks

[sinhrks]

Wow, great. Thanks!

[jreback]

merged via ead3ca8 (my change in another commit)

thanks!

I don't believe we had an issue assosicated, correct?

[sinhrks]

Though this was based on gitter chat, #5196 refers to the same issue. Closed.

[jreback]

@sinhrks awesome thanks!