GitHub user HyukjinKwon opened a pull request:
https://github.com/apache/spark/pull/22939
[SPARK-25446][R] Add schema_of_json() and schema_of_csv() to R
## What changes were proposed in this pull request?
This PR proposes to expose `schema_of_json` and `schema_of_csv` at R side.
**`schema_of_json`**:
```r
> json <- '{"name":"Bob"}'
> df <- sql("SELECT * FROM range(1)")
> head(select(df, schema_of_json(json)))
schema_of_json({"name":"Bob"})
1 struct<name:string>
```
**`schema_of_csv`**:
```r
> csv <- "Amsterdam,2018"
> df <- sql("SELECT * FROM range(1)")
> head(select(df, schema_of_csv(csv)))
schema_of_csv(Amsterdam,2018)
1 struct<_c0:string,_c1:int>
```
This is useful when it's used with [to|from]_[csv|json]:
```r
> df <- sql("SELECT named_struct('name', 'Bob') as people")
> df <- mutate(df, people_json = to_json(df$people))
> head(select(df, from_json(df$people_json,
schema_of_json(head(df)$people_json))))
from_json(people_json)
1 Bob
```
```r
> df <- sql("SELECT named_struct('name', 'Bob') as people")
> df <- mutate(df, people_json = to_csv(df$people))
> head(select(df, from_csv(df$people_json,
schema_of_csv(head(df)$people_json))))
from_csv(people_json)
1 Bob
```
## How was this patch tested?
Manually tested, unit tests added, documentation manually built and
verified.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/HyukjinKwon/spark SPARK-25446
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/22939.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 #22939
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commit c4a78fc0b14876a857bdd9b2f8f094744dd76c04
Author: hyukjinkwon <gurwls223@...>
Date: 2018-11-04T08:46:20Z
Add schema_of_json() and schema_of_csv() to R
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