change IGroup __repr__

If we want to return IGroup instead of LGroup for stuff like Axis/Group.startingwith,endingwith,... (see #438) we need to change IGroup __repr__ to somehow display the label the position corresponds to. Otherwise it makes it harder than necessary to debug any code using them. The problem is that I haven't found a way to add this without breaking the eval(repr(v)) == v which is unfortunate.

>>> a = Axis('a=a0..a5')
>>> # current situation
>>> a["a1,a3,a4"]
a['a1', 'a3', 'a4']
>>> a.i[1, 3, 4]
a.i[1, 3, 4]
>>> # alternative 1
>>> a.i[1, 3, 4]
a.i['a1' (1), 'a3' (3), 'a4' (4)]
>>> # alternative 2 -- this is more "pure" but looks less pretty
>>> a.i[1, 3, 4]
a.i[1 ('a1'), 3 ('a3'), 4 ('a4')]
>>> # alternative 3
>>> a.i[1, 3, 4]
a.i[1, 3, 4 ('a1', 'a3', 'a4')]
>>> # alternative 4
>>> a.i[1, 3, 4]
a.i[1, 3, 4] ('a1', 'a3', 'a4')
>>> # alternative 5 -- this is even more "pure" (we could make it evaluate correctly) but looks even less pretty
>>> a.i[1, 3, 4]
IGroup([1, 3, 4], axis=a, display=['a1', 'a3', 'a4'])

There are potentially many other alternatives. Please suggest them if you have any idea.

Two special problems

positional slices, for which the stop bound is not inclusive, which means that slices ending at the end of the axis are problematic (and other slices are unintuitive)

>>> a.i[1:6]
a.i[1 ('a1'): 6 (??)]
>>> # having 'a3' displayed (but not included) makes it more confusing
>>> a.i[1:3]
a.i[1 ('a1'): 3 ('a3')]
>>> # maybe doing a special case for slices would make sense (ie do not translate each bound separately but the whole "key":
>>> a.i[1:3]
a.i[1:3 ('a1':'a2')]

slices on axes with integer labels (especially if pos == label) are a bit confusing (but they are probably already confusing even though the confusion is hidden ;-)).

>>> a = Axis('a=0..10')
>>> # current
>>> a.i[1:3]
a.i[1:3]
>>> # each bound separately
>>> a.i[1:3]
a.i[1 (1): 3 (3)]
>>> # the whole key
>>> a.i[1:3]
a.i[1:3 (1:2)]

My current preference goes for alternative 4 (because it will be easier to copy-paste than alternative 3) and for slices, to translate the whole key instead of each bound separately.

Here is a concrete example when you would get an IGroup without explicitly asking for it:

>>> people = Axis(['Bruce Wayne', 'Bruce Willis', 'Arthur Dent'], 'people')
>>> group = people.startingwith('Bru')
>>> # current
>>> group
people['Bruce Wayne', 'Bruce Willis']
>>> # alternative 4
>>> group
people.i[0, 1] ('Bruce Wayne', 'Bruce Willis')
>>> # current
>>> group.containing('Will')
people['Bruce Willis']
>>> # alternative 4
>>> group.containing('Will')
people.i[1] ('Bruce Willis')

Yet another option is to blur the difference between IGroup and LGroup and only display the position in the presence of duplicate labels:

>>> people = Axis(['Bruce', 'Bruce', 'Bru'], 'people')
>>> group = people.startingwith('Bru')
>>> # current (which is broken and select the first or last 'Bruce' twice)
>>> group
people['Bruce', 'Bruce', 'Bru']
>>> # alternative 4
>>> group
people.i[0, 1, 2] ('Bruce', 'Bruce', 'Bru')
>>> # alternative 6. It is the nicest of all IMO but breaks eval(repr) badly 
>>> # when there is no duplicate, it is indistinguishable from an LGroup (which is both
>>> # a bad and a good thing)
>>> group
people['Bruce' (0), 'Bruce' (1), 'Bru']
>>> people.i[1, 2]
people['Bruce' (1), 'Bru']

My first choice is also alternative 4 (which, indeed, allows easy copy/paste) and to translate the whole key instead of each bound separately for slices.

I wouldn't "blur" the difference between PGroup and LGroup. It's good to know when you are dealing with PGroup or LGroup. Explicit is better than implicit.

I wonder if it wouldn't be simpler to just ensure we have no duplicate label on Axis construction (it would incur a performance penalty but I assume it would be very small -- or even negligible in our models I think) by deduplicating them:

Something like:

>>> Axis('test=a,a,a,a')
Axis(['a#0', 'a#1', 'a#2', 'a#3'], 'a')

or maybe start counting at 1??? Unsure what would be least confusing. See what Pandas does for columns.

Then we can always use IGroups (except for X.) but display them like LGroups

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change IGroup __repr__ #447

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gdementen commented on Sep 25, 2017

gdementen commented on Sep 25, 2017

alixdamman commented on Sep 25, 2017

gdementen commented on Mar 31, 2026

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change IGroup repr #447