来自 Scala 和 Apache Spark 上 csv 的空值答案

【问题标题】：Null values from a csv on Scala and Apache Spark来自 Scala 和 Apache Spark 上 csv 的空值
【发布时间】：2019-03-16 19:54:00
【问题描述】：

我使用的是 Apache Spark 2.3.0。当我上传一个 csv 文件然后我放 df.show 时，它会向我显示所有空值的表，我想知道为什么，因为 csv 中的一切看起来都很好

val df = sqlContext.read.format("com.databricks.spark.csv").option("header","true").schema(schema).load("data.csv")

val schema = StructType(Array(StructField("Rank",StringType,true),StructField("Grade", StringType, true),StructField("Channelname",StringType,true),StructField("Video Uploads",IntegerType,true), StructField("Suscribers",IntegerType,true),StructField("Videoviews",IntegerType,true)))

Rank,Grade,Channelname,VideoUploads,Subscribers,Videoviews
1st,A++ ,Zee TV,82757,18752951,20869786591
2nd,A++ ,T-Series,12661,61196302,47548839843
3rd,A++ ,Cocomelon - Nursery Rhymes,373,19238251,9793305082
4th,A++ ,SET India,27323,31180559,22675948293
5th,A++ ,WWE,36756,32852346,26273668433
6th,A++ ,Movieclips,30243,17149705,16618094724
7th,A++ ,netd mÃ¼zik,8500,11373567,23898730764
8th,A++ ,ABS-CBN Entertainment,100147,12149206,17202609850
9th,A++ ,Ryan ToysReview,1140,16082927,24518098041
10th,A++ ,Zee Marathi,74607,2841811,2591830307
11th,A+ ,5-Minute Crafts,2085,33492951,8587520379
12th,A+ ,Canal KondZilla,822,39409726,19291034467
13th,A+ ,Like Nastya Vlog,150,7662886,2540099931
14th,A+ ,Ozuna,50,18824912,8727783225
15th,A+ ,Wave Music,16119,15899764,10989179147
16th,A+ ,Ch3Thailand,49239,11569723,9388600275
17th,A+ ,WORLDSTARHIPHOP,4778,15830098,11102158475
18th,A+ ,Vlad and Nikita,53,-- ,1428274554

【问题讨论】：

文件中的分隔符是逗号(,)还是别的什么？
你能贴出csv文件的前几行吗？
@TerryDactyl 我在上面添加了它们

标签： scala csv apache-spark apache-spark-mllib

【解决方案1】：

null 值的原因是因为 csv API 的默认“模式”是PERMISSIVE：

mode（默认PERMISSIVE）：允许处理损坏的模式解析过程中的记录。它支持以下不区分大小写模式。
- PERMISSIVE ：当它遇到一个时将其他字段设置为空损坏的记录，并将格式错误的字符串放入字段中由 columnNameOfCorruptRecord 配置。为了保存损坏的记录，用户可以在一个名为 columnNameOfCorruptRecord 的字符串类型字段中设置一个用户定义的架构。如果架构没有该字段，则丢弃解析过程中损坏的记录。当解析的 CSV 令牌的长度为比模式的预期长度短，它将 null 设置为额外的字段。
- DROPMALFORMED：忽略整个损坏的记录。
- FAILFAST：遇到损坏的记录时抛出异常

csv API

【讨论】：

【解决方案2】：

因此，如果我们在没有架构的情况下加载，我们会看到以下内容：

scala> val df = spark.read.format("com.databricks.spark.csv").option("header","true").load("data.csv")

df: org.apache.spark.sql.DataFrame = [Rank: string, Grade: string ... 4 more fields]

scala> df.show
+----+-----+--------------------+------------+-----------+-----------+
|Rank|Grade|         Channelname|VideoUploads|Subscribers| Videoviews|
+----+-----+--------------------+------------+-----------+-----------+
| 1st| A++ |              Zee TV|       82757|   18752951|20869786591|
| 2nd| A++ |            T-Series|       12661|   61196302|47548839843|
| 3rd| A++ |Cocomelon - Nurse...|         373|   19238251| 9793305082|
| 4th| A++ |           SET India|       27323|   31180559|22675948293|
| 5th| A++ |                 WWE|       36756|   32852346|26273668433|
| 6th| A++ |          Movieclips|       30243|   17149705|16618094724|
| 7th| A++ |          netd müzik|        8500|   11373567|23898730764|
| 8th| A++ |ABS-CBN Entertain...|      100147|   12149206|17202609850|
| 9th| A++ |     Ryan ToysReview|        1140|   16082927|24518098041|
|10th| A++ |         Zee Marathi|       74607|    2841811| 2591830307|
|11th|  A+ |     5-Minute Crafts|        2085|   33492951| 8587520379|
|12th|  A+ |     Canal KondZilla|         822|   39409726|19291034467|
|13th|  A+ |    Like Nastya Vlog|         150|    7662886| 2540099931|
|14th|  A+ |               Ozuna|          50|   18824912| 8727783225|
|15th|  A+ |          Wave Music|       16119|   15899764|10989179147|
|16th|  A+ |         Ch3Thailand|       49239|   11569723| 9388600275|
|17th|  A+ |     WORLDSTARHIPHOP|        4778|   15830098|11102158475|
|18th|  A+ |     Vlad and Nikita|          53|        -- | 1428274554|
+----+-----+--------------------+------------+-----------+-----------+

如果我们应用您的架构，我们会看到：

scala> val schema = StructType(Array(StructField("Rank",StringType,true),StructField("Grade", StringType, true),StructField("Channelname",StringType,true),StructField("Video Uploads",IntegerType,true), StructField("Suscribers",IntegerType,true),StructField("Videoviews",IntegerType,true)))

scala> val df = spark.read.format("com.databricks.spark.csv").option("header","true").schema(schema).load("data.csv")
df: org.apache.spark.sql.DataFrame = [Rank: string, Grade: string ... 4 more fields]

scala> df.show
+----+-----+-----------+-------------+----------+----------+
|Rank|Grade|Channelname|Video Uploads|Suscribers|Videoviews|
+----+-----+-----------+-------------+----------+----------+
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
|null| null|       null|         null|      null|      null|
+----+-----+-----------+-------------+----------+----------+

现在，如果我们查看您的数据，我们会看到订阅者包含非整数值 ("--")，而视频视图包含超过整数最大值 (2,147,483,647) 的值

因此，如果我们更改架构以符合数据：

scala> val schema = StructType(Array(StructField("Rank",StringType,true),StructField("Grade", StringType, true),StructField("Channelname",StringType,true),StructField("Video Uploads",IntegerType,true), StructField("Suscribers",StringType,true),StructField("Videoviews",LongType,true)))
schema: org.apache.spark.sql.types.StructType = StructType(StructField(Rank,StringType,true), StructField(Grade,StringType,true), StructField(Channelname,StringType,true), StructField(Video Uploads,IntegerType,true), StructField(Suscribers,StringType,true), StructField(Videoviews,LongType,true))

scala> val df = spark.read.format("com.databricks.spark.csv").option("header","true").schema(schema).load("data.csv")
df: org.apache.spark.sql.DataFrame = [Rank: string, Grade: string ... 4 more fields]

scala> df.show
+----+-----+--------------------+-------------+----------+-----------+
|Rank|Grade|         Channelname|Video Uploads|Suscribers| Videoviews|
+----+-----+--------------------+-------------+----------+-----------+
| 1st| A++ |              Zee TV|        82757|  18752951|20869786591|
| 2nd| A++ |            T-Series|        12661|  61196302|47548839843|
| 3rd| A++ |Cocomelon - Nurse...|          373|  19238251| 9793305082|
| 4th| A++ |           SET India|        27323|  31180559|22675948293|
| 5th| A++ |                 WWE|        36756|  32852346|26273668433|
| 6th| A++ |          Movieclips|        30243|  17149705|16618094724|
| 7th| A++ |          netd müzik|         8500|  11373567|23898730764|
| 8th| A++ |ABS-CBN Entertain...|       100147|  12149206|17202609850|
| 9th| A++ |     Ryan ToysReview|         1140|  16082927|24518098041|
|10th| A++ |         Zee Marathi|        74607|   2841811| 2591830307|
|11th|  A+ |     5-Minute Crafts|         2085|  33492951| 8587520379|
|12th|  A+ |     Canal KondZilla|          822|  39409726|19291034467|
|13th|  A+ |    Like Nastya Vlog|          150|   7662886| 2540099931|
|14th|  A+ |               Ozuna|           50|  18824912| 8727783225|
|15th|  A+ |          Wave Music|        16119|  15899764|10989179147|
|16th|  A+ |         Ch3Thailand|        49239|  11569723| 9388600275|
|17th|  A+ |     WORLDSTARHIPHOP|         4778|  15830098|11102158475|
|18th|  A+ |     Vlad and Nikita|           53|       -- | 1428274554|
+----+-----+--------------------+-------------+----------+-----------+

【讨论】：