[jira] [Created] (ARROW-6338) [R] Type function names don't match type names

["Neal Richardson (Jira)" <ji...@apache.org>]

Neal Richardson created ARROW-6338:
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             Summary: [R] Type function names don't match type names
                 Key: ARROW-6338
                 URL: https://issues.apache.org/jira/browse/ARROW-6338
             Project: Apache Arrow
          Issue Type: Improvement
          Components: R
            Reporter: Neal Richardson
            Assignee: Neal Richardson
             Fix For: 0.15.0


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:
{code:r}
> 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 
{code}
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]

{code:r}
> schema(b = float64(), c = boolean(), d = utf8(), e = float32(), f = float16())
arrow::Schema 
b: double
c: bool
d: string
e: float
f: halffloat 
{code}

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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