API: allow option truncate for display.show_dimensions to only show dimensions if truncated (GH6457)

[jreback]

closes #6547

add the option 'trunctate'.
Should this be the new default?????

dfd = pd.DataFrame(np.arange(25).reshape(-1,5), index=[0,1,2,3,4], columns=[0,1,2,3,4])

# show dimensions only if truncated
with pd.option_context('display.max_rows', 2, 'display.max_columns', 2,  'display.show_dimensions', 'truncate'):
        print(dfd)

   0  1    
0  0  1 ...
1  5  6 ...
  .. ..    

[5 rows x 5 columns]

# show dimensions only if truncated
with pd.option_context('display.max_rows', 10, 'display.max_columns', 40, 'display.show_dimensions', 'truncate'):
        print(dfd)

    0   1   2   3   4
0   0   1   2   3   4
1   5   6   7   8   9
2  10  11  12  13  14
3  15  16  17  18  19
4  20  21  22  23  24

[jreback]

@jseabold @jorisvandenbossche @TomAugspurger @cpcloud

[TomAugspurger]

Should use print()! Same below.

[jreback]

right! thanks...

[TomAugspurger]

Looks good on a quick glance.

[jorisvandenbossche]

are the display.width and display.expand_frame_repr necessary here in the example?

[jreback]

not really except that I override these in my environement; so just want to ensure all options are setup to allow expanding (or not)

[jorisvandenbossche]

I see, but for the docs this won't be a problem I think. And now it is a bit overhead for the user to see what the relevant options are. So I would leave them out personally.

[jreback]

ok...makes sense

@jorisvandenbossche do you think this 'solves' the thread that @jseabold brought up?

[jorisvandenbossche]

small detail to nitpick, but truncated instead of truncate sounds better to me (as the option), as it is not really involved in the action of truncating, only the state of being truncated

[jreback]

@jorisvandenbossche I agree it sounds better, except, that large_repr uses truncate

and wanted to be consistent, but ok if you feel strongly

[jreback]

changed to use 'truncated' & example in v0.14.0.txt simpler

[jorisvandenbossche]

Ah, but if large_repr already uses the other, I am not feeling strongly about it.

@jreback about if this closes the issue that @jseabold brought up in #6547, he can maybe better say it himself, but I don't think it really does solve his issue he encountered in statsmodels (the use of dataframes to give back the overview result of a model, for which these dimensions are a bit superfluous/distracting). But as also said on the mailing list, not everybody's needs can be satisfied at the same time.
And this PR provides in any case all needed architecture. Given this, the discussion in the issue/on the mailing list, is only about what should be the default value of display.show_dimensions: True or truncated? True would be compatible with 0.13, truncated would be compatible with <=0.12 (for small dataframes).

[jreback]

ok..put back to 'truncate'.

like @jseabold to comment (and maybe should send to ML). but I think let's make the default 'truncate'.?

[TomAugspurger]

Posted on the ML. I tentatively vote for the default to be truncate(d). That really does fix the statsmodels issue.

[jreback]

thanks @TomAugspurger