Details
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Improvement
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Status: Resolved
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Major
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Resolution: Fixed
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None
Description
I noticed this while working on documentation for ARROW-5505, trying to show how you could pass an explicit schema definition to make a table. For a few types, the name of the type that gets printed (and comes from the C++ library) doesn't match the name of the function you use to specify the type in a schema:
> tab <- to_arrow(data.frame( + a = 1:10, + b = as.numeric(1:10), + c = sample(c(TRUE, FALSE, NA), 10, replace = TRUE), + d = letters[1:10], + stringsAsFactors = FALSE + )) > tab$schema arrow::Schema a: int32 b: double c: bool d: string # Alright, let's make that schema > schema(a = int32(), b = double(), c = bool(), d = string()) Error in bool() : could not find function "bool" # Hmm, ok, so bool --> boolean() > schema(a = int32(), b = double(), c = boolean(), d = string()) Error in string() : could not find function "string" # string --> utf8() > schema(a = int32(), b = double(), c = boolean(), d = utf8()) Error: type does not inherit from class arrow::DataType # Wha? > double() numeric(0) # Oh. double is a base R function. > schema(a = int32(), b = float64(), c = boolean(), d = utf8()) arrow::Schema a: int32 b: double c: bool d: string
If you believe this switch statement is correct, these three, along with float and half_float, are the only mismatches: https://github.com/apache/arrow/blob/master/r/R/R6.R#L81-L109
> schema(b = float64(), c = boolean(), d = utf8(), e = float32(), f = float16()) arrow::Schema b: double c: bool d: string e: float f: halffloat
I can add aliases (i.e. another function that does the same thing) for bool, string, float, and halffloat, and I can add some magic so that double() (and even integer()) work inside the schema() function. But in looking into the C++ side to confirm where these alternate type names were coming from, I saw some inconsistencies. For example, https://github.com/apache/arrow/blob/master/cpp/src/arrow/type.h#L773-L788 suggests that the StringType should report its name as "utf8". But the ToString method here https://github.com/apache/arrow/blob/master/cpp/src/arrow/type.cc#L191 has it report as "string". It's unclear why those should report differently.
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