Stuart White created SPARK-28058:
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Summary: Reading csv with DROPMALFORMED sometimes doesn't drop
malformed records
Key: SPARK-28058
URL: https://issues.apache.org/jira/browse/SPARK-28058
Project: Spark
Issue Type: Bug
Components: SQL
Affects Versions: 2.4.3, 2.4.1
Reporter: Stuart White
The spark sql csv reader is not dropping malformed records as expected.
Consider this file (fruit.csv). Notice it contains a header record, 3 valid
records, and one malformed record.
{noformat}
fruit,color,price,quantity
apple,red,1,3
banana,yellow,2,4
orange,orange,3,5
xxx
{noformat}
If I read this file using the spark sql csv reader as follows, everything looks
good. The malformed record is dropped.
{noformat}
scala> spark.read.option("header", "true").option("mode",
"DROPMALFORMED").csv("fruit.csv").show(truncate=false)
+------+------+-----+--------+
|fruit |color |price|quantity|
+------+------+-----+--------+
|apple |red |1 |3 |
|banana|yellow|2 |4 |
|orange|orange|3 |5 |
+------+------+-----+--------+
{noformat}
However, if I select a subset of the columns, the malformed record is not
dropped. The malformed data is placed in the first column, and the remaining
column(s) are filled with nulls.
{noformat}
scala> spark.read.option("header", "true").option("mode",
"DROPMALFORMED").csv("fruit.csv").select('fruit).show(truncate=false)
+------+
|fruit |
+------+
|apple |
|banana|
|orange|
|xxx |
+------+
scala> spark.read.option("header", "true").option("mode",
"DROPMALFORMED").csv("fruit.csv").select('fruit, 'color).show(truncate=false)
+------+------+
|fruit |color |
+------+------+
|apple |red |
|banana|yellow|
|orange|orange|
|xxx |null |
+------+------+
scala> spark.read.option("header", "true").option("mode",
"DROPMALFORMED").csv("fruit.csv").select('fruit, 'color,
'price).show(truncate=false)
+------+------+-----+
|fruit |color |price|
+------+------+-----+
|apple |red |1 |
|banana|yellow|2 |
|orange|orange|3 |
|xxx |null |null |
+------+------+-----+
{noformat}
And finally, if I manually select all of the columns, the malformed record is
once again dropped.
{noformat}
scala> spark.read.option("header", "true").option("mode",
"DROPMALFORMED").csv("fruit.csv").select('fruit, 'color, 'price,
'quantity).show(truncate=false)
+------+------+-----+--------+
|fruit |color |price|quantity|
+------+------+-----+--------+
|apple |red |1 |3 |
|banana|yellow|2 |4 |
|orange|orange|3 |5 |
+------+------+-----+--------+
{noformat}
I would expect the malformed record(s) to be dropped regardless of which
columns are being selected from the file.
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