API/ENH: create Interval class

[jreback]

xref #8595

something like: Interval(left=(-1.5,'open),right=(0,'closed'))

reprs to (-1.5,0]

can be used immediately in the index values for pd.cut and such (as an object index)
evenutally can form the basis for IntervalIndex

cc @shoyer
cc @JanSchulz
cc @rosnfeld

[shoyer]

Sounds good to me. As a reminder: here is the IntervalIndex proposal: #7640

Let's consider whether you should be able to control whether the level and right margins are closed/open separately or if you should only be able to say closed='left' or closed='right'. I am inclined to go for the later since it will be more complex for other cases in IntervalIndex.

[jreback]

@shoyer

you could also do

Interval(left,right,closed='left|right|both|neither') I guess for full compat (and could have both constructors I guess)

[jnmclarty]

Idea: def __init__(leftside='[',leftnum=0,rightnum=0,rightside=']')

Then...

Interval('[',left,right,']') == Interval('closed',left,right,'closed') == Interval(leftnum=left,rightnum=right)

could subclass and create left(leftside,leftnum) and right(rightnum, rightside), so that left('(',-1) + right(2,']') == Interval('(',-1,2,']')

...but individually they would repr to (-1,inf] and [-inf,2]

[shoyer]

One follow up thought: if we support closed='both' and closed='neither' we don't want the want the repr to look like [-1.5, 0] or (-1.5, 0). Probably better to repr to the more verbose Interval(-1.5, 0, closed='both') for these cases.

[jankatins]

Why this verbose repr? In repr of a dataframe (as index or values), I would expect that I only get the "short" repr...

[shoyer]

The problem is ambiguity with list and tuple, at least as long as the array has dtype=object.

On Tue, Oct 28, 2014 at 2:56 AM, Jan Schulz notifications@github.com
wrote:

Why this verbose repr? In repr of a dataframe (as index or values), I would expect that I only get the "short" repr...

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#8625 (comment)

[jnmclarty]

Could clear up the ambiguity with dash ( or even double dash ). Nobody should confuse "(0 - 2)" with a tuple. Nor would "[0 - 2]" be confused with a list.