<div dir="ltr"><div>> I think consistently propagating NA in comparison operations is a worthwhile goal.</div><div><br></div><div>That's an argument for having a three-valued bool-dtype, not for replacing all other NA-like values.<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Feb 17, 2020 at 8:34 AM Tom Augspurger <<a href="mailto:tom.augspurger88@gmail.com">tom.augspurger88@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">> 2) The "only one NA value is simpler" argument strikes me as a solution in search of a problem.<div><br></div><div>I don't think that's correct. I think consistently propagating NA in comparison operations is a worthwhile goal.<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Feb 17, 2020 at 10:25 AM Brock Mendel <<a href="mailto:jbrockmendel@gmail.com" target="_blank">jbrockmendel@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div>> It's not fully clear to me what you want to say with this, so a more
detailed clarification is welcome (I mean, I understand the sentence and
remember the discussion, but don't fully understand the point being
made in context, or in what direction you think more discussion is
needed). <br></div><div><br></div><div>I don't particularly think more discussion is needed, as this is a rehash of #28095, where this horse has already been beaten to death.<br></div><div><br></div><div>As Tom noted <a href="https://github.com/pandas-dev/pandas/issues/28095#issuecomment-537501744" target="_blank">here</a>, using pd.NA in places where we currently use NaT breaks the usual identity (that we rely on A LOT)<br></div><div><br></div><div>```<code>(array + array)[0].dtype <=> (array + array[0]).dtype</code>```<br><code></code></div></div><div><br></div><div>(Yes, this holds only imperfectly for NaT because NaT serves as both NotADatetime and NotATimedelta, and I'll refer you to the decomposing horse in #28095.)<br></div><div> </div><div>Also from #28095:</div><div><br></div><div>```Series[timedelta64] * pd.NaT``` unambiguously raises, but ```Series[timedelta64] * pd.NA``` could be timedelta64</div><div><br></div><div>> Assume we introduce a new "nullable datetime" dtype that uses a mask to
track NAs, and can still have NaT in the values. In practice, this still
means that we "replace NaT with NA"</div><div><br></div><div>This strikes me as contradictory. <br></div><div><br></div><div>> So do you mean: "in my opinion, we should not do this" (what I just
described above), because in practice that would mean breaking
arithmetic consistency? Or that if we want to start using NA for
datetimelike dtypes, you think "dtype-parametrized" NA values are
necessary (so you can distinguish NA[datetime] and NA[timedelta] ?)</div><div><br></div><div>I think:</div><div><br></div><div>1) pd.NA solves an _actual_ problem which is that we used to use np.nan in places (categorical, object) where np.nan was semantically misleading. <br></div><div> a) What these have in common is that they are in general non-arithmetic dtypes.</div><div> b) This is an improvement, and I'm glad you put in the effort to make it happen.</div><div> c) Trying to shoe-horn pd.NA into cases where it is semantically misleading based on the Highlander Principle is counter-productive.</div><div><br></div><div>2) The "only one NA value is simpler" argument strikes me as a solution in search of a problem.</div><div> a) All the more so if you want this to supplement np.nan/pd.NaT instead of replace them.</div><div> b) *the idea of replacing vs supplementing needs to be made much more explicit/clear*</div><div><br></div><div>3) The "dtype-parametrized" NA did come up in #28095, but I never advocated it.<br></div><div> a) I am open to separating out a NaTimedelta (xref #24983) from pd.NaT, and don't particularly care what it is called.</div><div><br></div><div><br></div><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Feb 17, 2020 at 3:37 AM Joris Van den Bossche <<a href="mailto:jorisvandenbossche@gmail.com" target="_blank">jorisvandenbossche@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>> This would also imply creating a nullable float dtype and making
our datelikes use NA rather than NaT too. That seemed to be generally
OK, but wasn't discussed too much.</div><div><br></div><div>My understanding of the discussion is that using a mask on top of datetimelike arrays would not _replace_ NaT, but supplement it with something semantically different. <br></div></blockquote><div><br></div><div>Yes, if we see it similar as NaNs for floats (where NaN is a specific float value in the data array, while NAs are tracked in the mask array), then for datetimelike arrays we can do something similar. And the same discussions about to what extent to distinguish NaN and NA or whether we need to provide options that we are going to have for float dtypes, will also be relevant for datetimelike dtypes (but then for NaT and NA). <br></div><div><br></div><div>But note that in practice, I <i>think</i> that the big majority of use cases will mostly use NA and not NaT in the data (eg when reading from files that have missing data). <br></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>Replacing NaT with NA breaks arithmetic consistency, as has been discussed ad nauseum.</div></blockquote></div><div><br></div><div>It's not fully clear to me what you want to say with this, so a more detailed clarification is welcome (I mean, I understand the sentence and remember the discussion, but don't fully understand the point being made in context, or in what direction you think more discussion is needed). <br></div><div><br></div><div>Assume we introduce a new "nullable datetime" dtype that uses a mask to track NAs, and can still have NaT in the values. In practice, this still means that we "replace NaT with NA" (because even though NaT is still possible, I think you would mostly get NAs as mentioned above; eg reading a file would now give NA instaed of NaT). </div><div>So do you mean: "in my opinion, we should not do this" (what I just described above), because in practice that would mean breaking arithmetic consistency? Or that if we want to start using NA for datetimelike dtypes, you think "dtype-parametrized" NA values are necessary (so you can distinguish NA[datetime] and NA[timedelta] ?)</div><div><br></div><div>Joris<br></div><div><br></div><div><br></div></div>
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