[ARROW-17462] [R] Cast scalars to type of field in Expression building

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 11.0.0
• Component/s: R
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/32726
• Assignee: Neal Richardson
• Reporter: Neal Richardson
• Created: 18/Aug/22 18:50
• Updated: 11/Jan/23 11:50
• Resolved: 31/Oct/22 15:24

Description

After looking at the ExecPlan output of some queries, it jumped out at me how we translate {{ int_field == 5 }} in R as {{ cast(int_field, float64) == 5 }} because 5 is a double in R.

This extra work has a noticeable performance impact. Here's a simple query on the taxi dataset, filtering down to 54 out of 1.5 billion rows and selecting a single column. My idea was to make a query that does not much other than evaluate the filter.

> system.time(ds |> select(passenger_count) |> filter(passenger_count > 10) |> compute())
   user  system elapsed 
  0.391   0.024   0.362 

> system.time(ds |> select(passenger_count) |> filter(passenger_count > Scalar$create(10, type = int8())) |> compute())
   user  system elapsed 
  0.206   0.025   0.179 

You can see the difference in the query plans too:

> ds |> select(passenger_count) |> filter(passenger_count > 10) |> explain()
ExecPlan with 4 nodes:
3:SinkNode{}
  2:ProjectNode{projection=[passenger_count]}
    1:FilterNode{filter=(cast(passenger_count, {to_type=double, allow_int_overflow=false, allow_time_truncate=false, allow_time_overflow=false, allow_decimal_truncate=false, allow_float_truncate=false, allow_invalid_utf8=false}) > 10)}
      0:SourceNode{}

> ds |> select(passenger_count) |> filter(passenger_count > Scalar$create(10, type = int8())) |> explain()
ExecPlan with 4 nodes:
3:SinkNode{}
  2:ProjectNode{projection=[passenger_count]}
    1:FilterNode{filter=(passenger_count > 10)}
      0:SourceNode{}

Ideally Acero would do this more intelligently (cf. ARROW-11402), but we should also be able to do smarter things when assembling the Expression in R.

Issue Links

• fixes: ARROW-18244 [R] `mutate(x2=ifelse(x=='',NA,x))` Error: Function 'if_else' has no kernel matching input types
• fixes: ARROW-13938 [C++] Date and datetime types should autocast from strings
• links to: GitHub Pull Request #13985