ARROW-13345: [C++] Add basic implementation for log to base b #10898
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Is it useful for the log base to be given as a |
@pitrou To be honest, I'm not sure if that such a scenario exists or whether that scenario is frequent. In any case, this draft was my first approach, and I can certainly change it to consider the base as a single value as a function option. Accordingly, I think that the base as a value makes more sense. |
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That seems pretty uncommon to me. I could contrive a few examples that aren't totally outlandish (say you're scaling/normalizing a value by groups, you might save the log base that you did the normalization with to be able to transform something back into the original values. But that's pretty contrived, and I bet most people would approach that with a lookup table and a for loop, basically. |
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I like having the option for the base to be an array. I suspect that in the vast majority of cases users will pass a scalar base, but this implementation is the most flexible way to do it. |
That sounds fine to me. |
| auto func = | ||
| std::make_shared<ArithmeticFloatingPointFunction>(name, Arity::Binary(), doc); | ||
| for (const auto& ty : FloatingPointTypes()) { | ||
| auto output = is_integer(ty->id()) ? float64() : ty; |
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nit: this line is redundant now (ty is never integer). I had filed ARROW-13361 to clean this up.
| @@ -1589,6 +1636,19 @@ const FunctionDoc log1p_checked_doc{ | |||
| "-inf or NaN."), | |||
| {"x"}}; | |||
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| const FunctionDoc logb_doc{ | |||
| "Compute log of x to base b of arguments element-wise", | |||
| ("Values <= -1 return -inf or NaN. Null values return null.\n" | |||
| } | ||
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| TYPED_TEST(TestBinaryArithmeticFloating, Log) { | ||
| // Integer arguments promoted to double, sanity check here |
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nit: I don't think this comment applies here
| this->AssertBinop(Logb, "[1.0, 10.0, null]", "[10.0, 10.0, null]", "[0.0, 1.0, null]"); | ||
| this->AssertBinop(Logb, "[1.0, 2.0, null]", "[2.0, 2.0, null]", "[0.0, 1.0, null]"); | ||
| this->AssertBinop(Logb, "[10.0, 100.0, 1000.0, null]", this->MakeScalar(10), | ||
| "[1.0, 2.0, 3.0, null]"); |
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We should also test what happens on Log of NaN, Inf, and -Inf. We should also check the error cases below here, with both check_overflow = true and check_overflow = false. Or really, it should look similar to the tests for the unary log functions here:
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More unit tests were added.
pitrou
changed the title
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@rommelDB Can you try to fix the build errors on Windows (see CI)? |
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LGTM. As Antoine notes, there's a build failure on Windows, you'll likely need a cast somewhere: https://github.com/apache/arrow/pull/10898/checks?check_run_id=3306264947#step:7:901
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Thanks for implementing this! |
Changes: