GitHub user HyukjinKwon opened a pull request:
https://github.com/apache/spark/pull/15354
[SPARK-17764][SQL] Add `to_json` supporting to convert nested struct column
to JSON string
## What changes were proposed in this pull request?
This PR proposes to add `to_json` function in contrast with `from_json` in
Scala, Java and Python.
It'd be useful if we can convert a same column from/to json. Also, some
datasources do not support nested types. If we are forced to save a dataframe
into those data sources, we might be able to work around by this function.
The usage is as below:
```scala
val df = Seq(Tuple1(Tuple1(1))).toDF("a")
df.select(to_json($"a").as("json")).show()
```
```bash
+--------+
| json|
+--------+
|{"_1":1}|
+--------+
```
## How was this patch tested?
Unit tests in `JsonFunctionsSuite` and `JsonExpressionsSuite`.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/HyukjinKwon/spark SPARK-17764
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15354.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 #15354
----
commit a33ac60902f233595158ed034b0fa49bcf9ac5ab
Author: hyukjinkwon <gurwls...@gmail.com>
Date: 2016-10-05T00:56:08Z
Initial implementation
commit d382b6364fd80a90375573e3fb68b9db2bf3cffb
Author: hyukjinkwon <gurwls...@gmail.com>
Date: 2016-10-05T02:42:00Z
Fix minor comment nits
commit eec0cd32bde8564a080da425be48986055523e8c
Author: hyukjinkwon <gurwls...@gmail.com>
Date: 2016-10-05T02:50:45Z
Add a missing dot
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