GitHub user wangmiao1981 opened a pull request:
https://github.com/apache/spark/pull/14613
[SPARK-16883][SparkR]:SQL decimal type is not properly cast to number when
collecting SparkDataFrame
## What changes were proposed in this pull request?
(Please fill in changes proposed in this fix)
registerTempTable(createDataFrame(iris), "iris")
str(collect(sql("select cast('1' as double) as x, cast('2' as decimal) as y
from iris limit 5")))
'data.frame': 5 obs. of 2 variables:
$ x: num 1 1 1 1 1
$ y:List of 5
..$ : num 2
..$ : num 2
..$ : num 2
..$ : num 2
..$ : num 2
The problem is that spark returns `decimal(10, 0)` col type, instead of
`decimal`. Thus, `decimal(10, 0)` is not handled correctly. It should be
handled as "double".
As discussed in JIRA thread, we can have two potential fixes:
1). Scala side fix to add a new case when writing the object back; However,
I can't use spark.sql.types._ in Spark core due to dependency issues. I don't
find a way of doing type case match;
2). SparkR side fix: Add a helper function to check special type like
`"decimal(10, 0)"` and replace it with `double`, which is PRIMITIVE type. This
special helper is generic for adding new types handling in the future.
I open this PR to discuss pros and cons of both approaches. If we want to
do Scala side fix, we need to find a way to match the case of DecimalType and
StructType in Spark Core.
## How was this patch tested?
(Please explain how this patch was tested. E.g. unit tests, integration
tests, manual tests)
Manual test:
> str(collect(sql("select cast('1' as double) as x, cast('2' as decimal) as
y from iris limit 5")))
'data.frame': 5 obs. of 2 variables:
$ x: num 1 1 1 1 1
$ y: num 2 2 2 2 2
R Unit tests
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/wangmiao1981/spark type
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/14613.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #14613
----
commit e95f5575018d15782917b9b3d679b4f6da345ee6
Author: [email protected] <[email protected]>
Date: 2016-08-11T23:15:15Z
add a type check helper
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