Support Questions
Find answers, ask questions, and share your expertise
Announcements
Alert: Welcome to the Unified Cloudera Community. Former HCC members be sure to read and learn how to activate your account here.

How to apply Regex pattern on a Dataframe's String columns in scala?

How to apply Regex pattern on a Dataframe's String columns in scala?

Contributor

I have a dataframe yeadDF, created by reading an RDBMS table as below:

val yearDF = spark.read.format("jdbc").option("url", connectionUrl)
                                                .option("dbtable", s"(${query}) as year2017")
                                                .option("user", devUserName)
                                                .option("password", devPassword)
                                                .option("numPartitions",15)
                                                .load()

I have to apply a regex pattern to the above dataframe before ingesting it into Hive table on HDFS. Below is the regex pattern:

regexp_replace(regexp_replace(regexp_replace(regexp_replace(regexp_replace(%s, E'[\\\\n]+', ' ', 'g' ), E'[\\\\r]+', ' ', 'g' ), E'[\\\\t]+', ' ', 'g' ), E'[\\\\cA]+', ' ', 'g' ), E'[\\\\ca]+', ' ', 'g' )

I should be applying this regex only on the columns that are of datatype String in the dataframe:

yearDF

. I tried the following way:

val regExpr = yearDF.schema.fields.map(x => if(x.dataType == String)
"regexp_replace(regexp_replace(regexp_replace(regexp_replace(regexp_replace(%s, E'[\\\\n]+', ' ', 'g' ), E'[\\\\r]+', ' ', 'g' ), E'[\\\\t]+', ' ', 'g' ), E'[\\\\cA]+', ' ', 'g' ), E'[\\\\ca]+', ' ', 'g' ) as %s".format(x,x))
yearDF.selectExpr(regExpr:_*)

But it gives me a compilation error:

Type mismatch, expected: Seq[String], actual: Array[Any]

 

I cannot use: 

yearDF.columns.map

as this will act on all the columns and I am unable to properly form the logic here. Could anyone let me know how can I apply the regex mentioned above on the dataframe:yearDF only on the columns that are of String type ?

 

2 REPLIES 2
Highlighted

Re: How to apply Regex pattern on a Dataframe's String columns in scala?

Master Collaborator

I assume the type mismatch is because you dont have defined the else in the if statement.

Then the result is just Any.

 

Type mismatch, expected: Seq[String], actual: Array[Any]

 

 

val regExpr = yearDF.schema.fields.map(x => if(x.dataType == String) { your_regex(x) } else { some_expression_returning_string } )
yearDF.selectExpr(regExpr:_*)

Re: How to apply Regex pattern on a Dataframe's String columns in scala?

New Contributor

Hi,

I also faced similar issues while applying regex_replace() to only strings columns of a dataframe.
The trick is to make regEx pattern (in my case "pattern") that resolves inside the double quotes and also apply escape characters.

val pattern="\"\\\\[\\\\x{FFFD}\\\\x{0}\\\\x{1F}\\\\x{81}\\\\x{8D}\\\\x{8F}\\\\x{90}\\\\x{9D}\\\\x{A0}\\\\x{0380}\\\\]\""

val regExpr = parq_out_df_temp.schema.fields.map(x =>
if(x.dataType == StringType){"regexp_replace(%s, $pattern,'') as %s".format(x.name,x.name)}
else x.name)

val parq_out=parq_out_df_temp.selectExpr(regExpr:_*)

 

This worked fine for me !!

Don't have an account?
Coming from Hortonworks? Activate your account here