I need to append only those who has non null values in pyspark dataframe

I am having the pyspark dataframe (df) having below sample table (table1): id, col1, col2, col3 1, abc, null, def 2, null, def, abc 3, def, abc, null

I am trying to get new column (final) by appending the all the columns by ignoring null values. I have tried pyspark code and used f.array(col1, col2, col3). Values are getting appended but it not ignoring null values. I have also tried UDF to append only non null columns but it is not working.

import pyspark.sql.functions as f    
df = spark.table('table1')
df = df.withColumn('final', f.array(col1,col2,col3))

Actual result:
id, col1, col2, col3, final
1, abc, null, def, [abc,,def]
2, null, def, abc, [,def, abc]
3, def, abc, null, [def,abc,,]

expected result:
id, col1, col2, col3, final
1, abc, null, def, [abc,def]
2, null, def, abc, [def, abc]
3, def, abc, null, [def,abc]


my col1, col2, col3 schema are as below:
where as col1 name is applications


applications: struct (nullable = false)
    applicationid: string (nullable = true)
    createdat: string (nullable = true)
    updatedat: string (nullable = true)
    source_name: string (nullable = true)
    status: string (nullable = true)
    creditbureautypeid: string (nullable = true)
    score: integer (nullable = true)
    applicationcreditreportid: string (nullable = true)
    firstname: string (nullable = false)
    lastname: string (nullable = false)
    dateofbirth: string (nullable = false)
    accounts: array (nullable = true)
        element: struct (containsNull = true)
        applicationcreditreportaccountid: string (nullable = true)
        currentbalance: integer (nullable = true)
        institutionid: string (nullable = true)
        accounttypeid: string (nullable = true)
        dayspastdue: integer (nullable = true)
        institution_name: string (nullable = true)
        account_type_name: string (nullable = true) 

please let me know if question is not clear or any more info is required. Any help would be appreciated. :)

Answer

Since Spark 2.4 you can use Higher Order Functions to do that (there is no UDF needed). In PySpark the query can look like this:

result = (
    df
    .withColumn("temp", f.array("col1", "col2", "col3"))
    .withColumn("final", f.expr("FILTER(temp, x -> x is not null)"))
    .drop("temp")
)