GitHub user HyukjinKwon opened a pull request:
https://github.com/apache/spark/pull/14745
[SPARK-16896][SQL] Handle duplicated field names in header consistently
with null or empty strings in CSV
## What changes were proposed in this pull request?
Currently, CSV datasource allows to load duplicated empty string fields or
fields having `nullValue` in the header. It'd be great if this can deal with
normal fields as well.
BTW, in the JIRA, there is a good reference, `read.csv()` in R. So, I
initially wanted to propose the similar behaviour.
In case of R, the CSV data below:
```
fieldA,fieldB,fieldA,fieldA
1,2,3,4
```
is parsed as below:
```r
test <- read.csv(file="test.csv",head=TRUE,sep=",")
> test
fieldA fieldB X fieldA.1 fieldA.2 X.1 X.2
1 1 2 3 4 5 6 7
```
However, Spark CSV datasource already is handling duplicated empty strings
and `nullValue` as field names. So the data below:
```
,,,fieldA,,fieldB,
1,2,3,4,5,6,7
```
is parsed as below:
```scala
spark.read.format("csv").option("header", "true").load("test.csv").show()
```
```
+---+---+---+------+---+------+---+
|_c0|_c1|_c2|fieldA|_c4|fieldB|_c6|
+---+---+---+------+---+------+---+
| 1| 2| 3| 4| 5| 6| 7|
+---+---+---+------+---+------+---+
```
To cut this short,
Here, R adds the number for each duplicate but Spark adds the number for
its position for all fields. Therefore, this PR proposes handling the
duplicates consistently with the existing behaviour as below:
data below:
```
fieldA,fieldB,fieldA,fieldA
1,2,3,4
```
is parsed as below:
```scala
spark.read.format("csv").option("header", "true").load("test.csv").show()
```
```
+-------+------+---+-------+-------+---+---+
|fieldA0|fieldB|_c2|fieldA3|fieldA4|_c5|_c6|
+-------+------+---+-------+-------+---+---+
| 1| 2| 3| 4| 5| 6| 7|
+-------+------+---+-------+-------+---+---+
```
## How was this patch tested?
Unit test in `CSVSuite`.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/HyukjinKwon/spark SPARK-16896
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/14745.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 #14745
----
commit 0d31ba7da9c88dcf87ef711e077b37778651aa2b
Author: hyukjinkwon <gurwls...@gmail.com>
Date: 2016-08-22T04:17:44Z
Load duplicated field names consistently with null or empty strings
commit a3c3dc6231429b4969baa800ba778ddf0f0aaf12
Author: hyukjinkwon <gurwls...@gmail.com>
Date: 2016-08-22T04:21:52Z
Fix style nits
----
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