问题
I am trying to read a csv file into a dataframe. I know what the schema of my dataframe should be since I know my csv file. Also I am using spark csv package to read the file. I trying to specify the schema like below.
val pagecount = sqlContext.read.format(\"csv\")
.option(\"delimiter\",\" \").option(\"quote\",\"\")
.option(\"schema\",\"project: string ,article: string ,requests: integer ,bytes_served: long\")
.load(\"dbfs:/databricks-datasets/wikipedia-datasets/data-001/pagecounts/sample/pagecounts-20151124-170000\")
But when I check the schema of the data frame I created, it seems to have taken its own schema. Am I doing anything wrong ? how to make spark to pick up the schema I mentioned ?
> pagecount.printSchema
root
|-- _c0: string (nullable = true)
|-- _c1: string (nullable = true)
|-- _c2: string (nullable = true)
|-- _c3: string (nullable = true)
回答1:
Try the below code, you need not specify the schema. When you give inferSchema as true it should take it from your csv file.
val pagecount = sqlContext.read.format("csv")
.option("delimiter"," ").option("quote","")
.option("header", "true")
.option("inferSchema", "true")
.load("dbfs:/databricks-datasets/wikipedia-datasets/data-001/pagecounts/sample/pagecounts-20151124-170000")
If you want to manually specify the schema, you can do it as below:
import org.apache.spark.sql.types._
val customSchema = StructType(Array(
StructField("project", StringType, true),
StructField("article", StringType, true),
StructField("requests", IntegerType, true),
StructField("bytes_served", DoubleType, true))
)
val pagecount = sqlContext.read.format("csv")
.option("delimiter"," ").option("quote","")
.option("header", "true")
.schema(customSchema)
.load("dbfs:/databricks-datasets/wikipedia-datasets/data-001/pagecounts/sample/pagecounts-20151124-170000")
回答2:
I'm using the solution provided by Arunakiran Nulu in my analysis (see the code). Despite it is able to assign the correct types to the columns, all the values returned are null. Previously, I've tried to the option .option("inferSchema", "true") and it returns the correct values in the dataframe (although different type).
val customSchema = StructType(Array(
StructField("numicu", StringType, true),
StructField("fecha_solicitud", TimestampType, true),
StructField("codtecnica", StringType, true),
StructField("tecnica", StringType, true),
StructField("finexploracion", TimestampType, true),
StructField("ultimavalidacioninforme", TimestampType, true),
StructField("validador", StringType, true)))
val df_explo = spark.read
.format("csv")
.option("header", "true")
.option("delimiter", "\t")
.option("timestampFormat", "yyyy/MM/dd HH:mm:ss")
.schema(customSchema)
.load(filename)
Result
root
|-- numicu: string (nullable = true)
|-- fecha_solicitud: timestamp (nullable = true)
|-- codtecnica: string (nullable = true)
|-- tecnica: string (nullable = true)
|-- finexploracion: timestamp (nullable = true)
|-- ultimavalidacioninforme: timestamp (nullable = true)
|-- validador: string (nullable = true)
and the table is:
|numicu|fecha_solicitud|codtecnica|tecnica|finexploracion|ultimavalidacioninforme|validador|
+------+---------------+----------+-------+--------------+-----------------------+---------+
| 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|
回答3:
For those interested in doing this in Python here is a working version.
customSchema = StructType([
StructField("IDGC", StringType(), True),
StructField("SEARCHNAME", StringType(), True),
StructField("PRICE", DoubleType(), True)
])
productDF = spark.read.load('/home/ForTesting/testProduct.csv', format="csv", header="true", sep='|', schema=customSchema)
testProduct.csv
ID|SEARCHNAME|PRICE
6607|EFKTON75LIN|890.88
6612|EFKTON100HEN|55.66
Hope this helps.
回答4:
Thanks to the answer by @Nulu, it works for pyspark with minimal tweaking
from pyspark.sql.types import LongType, StringType, StructField, StructType, BooleanType, ArrayType, IntegerType
customSchema = StructType(Array(
StructField("project", StringType, true),
StructField("article", StringType, true),
StructField("requests", IntegerType, true),
StructField("bytes_served", DoubleType, true)))
pagecount = sc.read.format("com.databricks.spark.csv")
.option("delimiter"," ")
.option("quote","")
.option("header", "false")
.schema(customSchema)
.load("dbfs:/databricks-datasets/wikipedia-datasets/data-001/pagecounts/sample/pagecounts-20151124-170000")
回答5:
Here's how you can work with a custom schema, a complete demo:
$> shell code,
echo "
Slingo, iOS
Slingo, Android
" > game.csv
Scala code:
import org.apache.spark.sql.types._
val customSchema = StructType(Array(
StructField("game_id", StringType, true),
StructField("os_id", StringType, true)
))
val csv_df = spark.read.format("csv").schema(customSchema).load("game.csv")
csv_df.show
csv_df.orderBy(asc("game_id"), desc("os_id")).show
csv_df.createOrReplaceTempView("game_view")
val sort_df = sql("select * from game_view order by game_id, os_id desc")
sort_df.show
回答6:
This is one of option where we can pass the column names to the dataframe while loading CSV.
import pandas
names = ['sepal-length', 'sepal-width', 'petal-length', 'petal-width', 'class']
dataset = pandas.read_csv("C:/Users/NS00606317/Downloads/Iris.csv", names=names, header=0)
print(dataset.head(10))
Output
sepal-length sepal-width petal-length petal-width class
1 5.1 3.5 1.4 0.2 Iris-setosa
2 4.9 3.0 1.4 0.2 Iris-setosa
3 4.7 3.2 1.3 0.2 Iris-setosa
4 4.6 3.1 1.5 0.2 Iris-setosa
5 5.0 3.6 1.4 0.2 Iris-setosa
6 5.4 3.9 1.7 0.4 Iris-setosa
7 4.6 3.4 1.4 0.3 Iris-setosa
8 5.0 3.4 1.5 0.2 Iris-setosa
9 4.4 2.9 1.4 0.2 Iris-setosa
10 4.9 3.1 1.5 0.1 Iris-setosa
回答7:
// import Library
import java.io.StringReader ;
import au.com.bytecode.opencsv.CSVReader
//filename
var train_csv = "/Path/train.csv";
//read as text file
val train_rdd = sc.textFile(train_csv)
//use string reader to convert in proper format
var full_train_data = train_rdd.map{line => var csvReader = new CSVReader(new StringReader(line)) ; csvReader.readNext(); }
//declares types
type s = String
// declare case class for schema
case class trainSchema (Loan_ID :s ,Gender :s, Married :s, Dependents :s,Education :s,Self_Employed :s,ApplicantIncome :s,CoapplicantIncome :s,
LoanAmount :s,Loan_Amount_Term :s, Credit_History :s, Property_Area :s,Loan_Status :s)
//create DF RDD with custom schema
var full_train_data_with_schema = full_train_data.mapPartitionsWithIndex{(idx,itr)=> if (idx==0) itr.drop(1);
itr.toList.map(x=> trainSchema(x(0),x(1),x(2),x(3),x(4),x(5),x(6),x(7),x(8),x(9),x(10),x(11),x(12))).iterator }.toDF
回答8:
schema definition as simple string
Just in case if some one is interested in schema definition as simple string with date and time stamp
data file creation from Terminal or shell
echo "
2019-07-02 22:11:11.000999, 01/01/2019, Suresh, abc
2019-01-02 22:11:11.000001, 01/01/2020, Aadi, xyz
" > data.csv
Defining the schema as String
user_schema = 'timesta TIMESTAMP,date DATE,first_name STRING , last_name STRING'
reading the data
df = spark.read.csv(path='data.csv', schema = user_schema, sep=',', dateFormat='MM/dd/yyyy',timestampFormat='yyyy-MM-dd HH:mm:ss.SSSSSS')
df.show(10, False)
+-----------------------+----------+----------+---------+
|timesta |date |first_name|last_name|
+-----------------------+----------+----------+---------+
|2019-07-02 22:11:11.999|2019-01-01| Suresh | abc |
|2019-01-02 22:11:11.001|2020-01-01| Aadi | xyz |
+-----------------------+----------+----------+---------+
Please note defining the schema explicitly instead of letting spark infer the schema also improves the spark read performance.
回答9:
In pyspark 2.4 onwards, you can simply use header parameter to set the correct header:
data = spark.read.csv('data.csv', header=True)
Similarly, if using scala you can use header parameter as well.
回答10:
here my solution is:
import org.apache.spark.sql.types._
val spark = org.apache.spark.sql.SparkSession.builder.
master("local[*]").
appName("Spark CSV Reader").
getOrCreate()
val movie_rating_schema = StructType(Array(
StructField("UserID", IntegerType, true),
StructField("MovieID", IntegerType, true),
StructField("Rating", DoubleType, true),
StructField("Timestamp", TimestampType, true)))
val df_ratings: DataFrame = spark.read.format("csv").
option("header", "true").
option("mode", "DROPMALFORMED").
option("delimiter", ",").
//option("inferSchema", "true").
option("nullValue", "null").
schema(movie_rating_schema).
load(args(0)) //"file:///home/hadoop/spark-workspace/data/ml-20m/ratings.csv"
val movie_avg_scores = df_ratings.rdd.map(_.toString()).
map(line => {
// drop "[", "]" and then split the str
val fileds = line.substring(1, line.length() - 1).split(",")
//extract (movie id, average rating)
(fileds(1).toInt, fileds(2).toDouble)
}).
groupByKey().
map(data => {
val avg: Double = data._2.sum / data._2.size
(data._1, avg)
})
来源：https://stackoverflow.com/questions/39926411/provide-schema-while-reading-csv-file-as-a-dataframe