feat(ir): add StringSlice
#8832
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NickCrews
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| │ ric │ | ||
| └───────────────────────┘ | ||
| ┏━━━━━━━━━━━━━━━━━━━━━━┓ | ||
| ┃ StringSlice(food, 3) ┃ |
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this repr isn't great: both [:3] and [3:] result in StringSlice(food, 3). But that is separate problem.
| ], | ||
| ) | ||
| def test_string(backend, alltypes, df, result_func, expected_func): | ||
| expr = result_func(alltypes).name("tmp") | ||
| def test_substring(backend, alltypes, df, result_func, expected_func): |
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the diff for these test cases is really messy, sorry. What I did:
- move some test cases to separate test_substring test
- remove xfails/brokens marks since I fixed/implemented things in polars and mssql
- removed no test cases
- added the
positive-indextest case
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Thanks for the explanation, I was going to ask why you deleted test cases 😂
Fixes ibis-project#8796 This also improves the compilation for Substring: - the bigquery, clickhouse, and datafusion implementations can just get deleted, they do the same thing as the base SqlGlotCompiler - The mssql compiler didn't actually compile Substring(arg, start, None) properly, it created the simple `substr(arg, len)` SQL function, but in mssql the length is always required. So fix that unrelated bug. - Optimizes the SQL generated by visit_Substring: Before, the generated SQL was of the form `if start >= 1 then substr(arg, start, length) else substr(arg, start+len(arg), length)`. Now, it is like `substring(arg, if start >= 1 then start else start+len(arg), length)`. This reduces the number of appearances of arg from 3 to 2. In general we want to shrink the args of the ifelses to as small as possible. - Add in the check for negative literal lengths to the SqlGlotCompiler
| stop = self.length() | ||
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| return self.substr(start, stop - start) | ||
| if start is not None and not isinstance(start, ir.Expr) and start < 0: |
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Is there a test case for this? Might be good to add one if there isn't. Same for the other seemingly uncovered lines below.
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there is not currently a test case. Agreed should add one. In this PR or a followup?
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I'll regenerate the snowflake snapshots. |
| return ops.Substring(_.arg, start=0, length=_.end) | ||
| if ( | ||
| isinstance(_.start, ops.Literal) | ||
| and isinstance(_.start.value, int) |
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The rewrite rule is good as is, just noting that this could be spelled as a pattern as well: p.StringSlice(p.Literal(int), p.Literal(int).
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As in there would be a different rule for each of the patterns? (Literal, None), (None, literal), (literal, literal)? Maybe a full example of how this could be spelled? If there are different rules then would I need to import three different rewrites in all the compilers?
I'd love to learn for next time.
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I think this is ideal in this current scenario, just wanted to highlight you that nested patterns are also supported.
There are various ways to spell this, here is a more complicated one showing what can be done with the rewrite system:
from ibis.expr.rewrites import p, d
p.StringSlice(end=None) >> d.Substring(_.arg, start=_.start) |
p.StringSlice(start=None) >> d.Substring(_.arg, start=0, length=_.end) |
p.StringSlice(p.Literal(int), p.Literal(int)) >> d.Substring(_.arg, start=_.start, length=_.end.value - _.start.value) |
p.StringSlice >> d.Substring(_.arg, start=_.start, length=d.Subtract(_.end, _.start)
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Thanks @NickCrews! |
Fixes #8796