feat: improve map(), struct(), array() #8666

NickCrews · 2024-03-15T16:42:17Z

This does a lot of changes. It was hard for me to separate them out as I implemented them. But now that it's all hashed out, I can try to split this up into separate commits if you want. But that might be sorta hard in
some cases.

Changes:

This is adding support for passing in None to all these constructors.
These use the new ibis.null(<type>) API to return op.Literal(None, <type>)s

Make these constructors idempotent: you can pass in existing Expressions into array(), etc.
The type argument for all of these now always has an effect, not just when passing in python literals. So basically it acts like a cast.

A big structural change is that now ops.Array has an optional
attribute "dtype", so if you pass in a 0-length sequence
of values the op still knows what dtype it is.

Several of the backends were always broken here, they just weren't getting caught. I marked them as broken, we can fix them in a followup.

You can test this locally with eg
pytest -m <backend> -k factory ibis/backends/tests/test_array.py ibis/backends/tests/test_map.py ibis/backends/tests/test_struct.py

Also, fix executing Literal(None) on pandas and polars, 0-length arrays on polars

Next steps

A possible nice follow-up would be to completely remove supporting structs, arrays, and maps inside ops.Literal.
Currently, when someone calls ibis.array([1,2]), that now results in ops.Array, but if they do ibis.literal([1,2]), it is represented as ops.Literal. It would be nice if inside ibis.literal() there was some logic like

...
if isinstance(val, Mapping):
    return ibis.map(val)
if is_iterable(val):
    return ibis.array(val)
...

and then all the backends wouldn't have to even worry about supporting these nested types in visit_Literal()

jcrist

Makes sense to me. Can you add a few tests in the appropriate ibis/tests/expr/test_{dtype}.py files?

Also curious - what was the use case that led to you wanting this change?

NickCrews · 2024-03-15T17:32:51Z

in my first attempt at #8649, I went about it the wrong way, but I needed to ensure something was an Array, but the incoming thing might already have been an array.

NickCrews · 2024-03-15T19:18:08Z

OK, as I added those tests I found some problems, and this snowballed into also being a fix for #8289. The implementations for both of these things are somewhat intertwined. It would be a pain to fix one, and then just change it again to fixx the other. So I just did everything at once.

ibis/expr/types/maps.py

ibis/expr/types/arrays.py

ibis/backends/tests/test_struct.py

ibis/backends/tests/test_array.py

ibis/backends/tests/test_map.py

ibis/expr/types/maps.py

ibis/expr/types/structs.py

ibis/formats/pandas.py

ibis/backends/tests/test_array.py

ibis/backends/pandas/convert.py

NickCrews · 2024-03-22T04:15:54Z

My goodness this gotten a bit out of hand.

EDIT: actually in the latest version it's not so bad. I didn't need to overhaul the internal representation after all.

OK I just pushed an absolute doozy of a commit in 530fad0. Curious how many backends that fails on. It required really overhauling the internal representation of ops.Array and ops.Struct to be able to distinguish between

the overall value is NULL
the contained values is NULL
Take a look at that commit description.

ncclementi · 2024-04-30T20:35:03Z

Hi @NickCrews, checking in here. What's the status on this one? It looks like there are a lot of conflicts and red on CI 😅 .

NickCrews · 2024-05-01T05:48:24Z

Yeeesssss this needs a bit of love :) Once my other pr with .cases lands I figured I would pick this up again.

Preparing for ibis-project#8666

Preparing for #8666

fixes ibis-project#8289 This does a lot of changes. It was hard for me to separate them out as I implemented them. But now that it's all hashed out, I can try to split this up into separate commits if you want. But that might be sorta hard in some cases. One this is adding support for passing in None to all these constructors. These use the new `ibis.null(<type>)` API to return `op.Literal(None, <type>)`s Make these constructors idempotent: you can pass in existing Expressions into array(), etc. The type argument for all of these now always has an effect, not just when passing in python literals. So basically it acts like a cast. A big structural change is that now ops.Array has an optional attribute "dtype", so if you pass in a 0-length sequence of values the op still knows what dtype it is. Several of the backends were always broken here, they just weren't getting caught. I marked them as broken, we can fix them in a followup. You can test this locally with eg `pytest -m <backend> -k factory ibis/backends/tests/test_array.py ibis/backends/tests/test_map.py ibis/backends/tests/test_struct.py` Also, fix executing Literal(None) on pandas and polars, 0-length arrays on polars Also, fixing converting dtypes on clickhouse, Structs should be converted to nonnullable dtypes.

moving towards ibis-project#8666

cpcloud · 2024-06-13T13:23:56Z

ibis/backends/sql/compiler.py

-    def visit_Array(self, op, *, exprs):
-        return self.f.array(*exprs)
+    def visit_Array(self, op, *, exprs, dtype):
+        return self.cast(self.f.array(*exprs), dtype)


This seems extraordinarily heavy-handed and overly broad.

Do we really need to cast the entire on constructing an array, for all SQL backends?

cpcloud · 2024-06-13T13:27:42Z

This PR is still too big. Can you split the array, map and struct implementations into three separate PRs?

NickCrews · 2024-06-13T14:46:21Z

Yeah splitting it probably is good.

map is easy, no semantic changes going on there
for struct, I want to add tests for empty structs. Therefore I think we need to decide on and merge my other PR regarding this behavior
for arrays, it's gonna be a little hairy too, because I am implementing empty arrays at the same time as adjusting the API. I don't really want to do them separately or it will just be churn. Unless you see a decent way to address those two things separately

cpcloud · 2024-06-27T11:00:08Z

@NickCrews Just checking in here, can you split these up some more?

NickCrews · 2024-06-27T19:37:21Z

OK, I just tried to split the struct and the map stuff into their own PRs, but both of those rely on the new ibis.array(arg, typ) API. So we need to get the array stuff in first. I'll split that out.

Picking out the array stuff from ibis-project#8666

NickCrews · 2024-06-27T19:47:52Z

split this into

Picking out the array stuff from ibis-project#8666

Picking out the array stuff from ibis-project#8666 Instead of trying to fit the two cases of 0-length and 1+ length arrays into the same op, I split them up into separate ones. By doing this, if we guarantee that all the elements of ops.Array() have the right type before construction, we don't have to do any fancy casting during compilation, all the elements will already have been casted as needed. This allows for the compilation of array<structs> on some sql backends like postgres. If we tried to cast the entire array, you end up with SQL like `cast [..] as STRUCT<...>[]`, which postgres freaks about. Instead, if we cast each individual element, such as `[cast({...} as ROW..., cast({...} as ROW...]`, then this is valid SQL. I added a Length annotation to ops.Array to verify the length is 1+. IDK, this isn't really needed, since if you ever did construct one, then the rlz.highest_precedence_dtype([]) would fail. But that might fail at a later time, and I wanted to raise an error at construction time. But, end users should never be constructing ops.Arrays directly, so this is a guardrail just for us ibis devs. So IDK, we could remove it, but I think it is a nice hint for future us.

jcrist reviewed Mar 15, 2024

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fix(duckdb): workaround for duckdb Map NULL bugs #8649

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bug: execution of struct literals in the pandas and dask backends returns the wrong value #8687

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feat: Support type arg to ibis.array and ibis.map #8289

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[meta] Ibis expression API stability #8996

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NickCrews changed the title ~~feat: make map(), struct(), array() idempotent~~ feat: improve map(), struct(), array() behave nicer May 9, 2024

NickCrews changed the title ~~feat: improve map(), struct(), array() behave nicer~~ feat: improve map(), struct(), array() May 10, 2024

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This was referenced Jun 6, 2024

test: disallow empty structs #9310

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test(sql): do more than a smoketest in test_literal() #9320

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test(refactor): simplify expr/test_literal.py #9321

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test(refactor): simplify expr/test_literal.py

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Preparing for ibis-project#8666

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test(refactor): simplify expr/test_literal.py

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Preparing for #8666

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chore(refactor): handle 0-length args in highest_precedence_shape()

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moving towards ibis-project#8666

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chore(refactor): handle 0-length args in highest_precedence_shape() #9333

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fix(datatypes): infer the correct shape for many existing ops #9334

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feat(api): improve ibis.array() #9458

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feat: support empty arrays, improve ibis.array() API #9473

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