Get Databricks Databricks-Certified-Associate-Developer-for-Apache-Spark-3.0 Exam Dumps

Answer : D

Correct code block:

schema = StructType([

StructField('itemId', IntegerType(), True),

StructField('attributes', ArrayType(StringType(), True), True),

StructField('supplier', StringType(), True)

])

spark.read.options(modifiedBefore='2029-03-20T05:44:46').schema(schema).parquet(filePath)

This Question: is more difficult than what you would encounter in the exam. In the exam, for this Question: type, only one error needs to be identified and not 'one or multiple' as in the

question.

Columns in the schema definition use the wrong object type, the modification date threshold is specified incorrectly, and Spark cannot identify the file format.

Correct! Columns in the schema definition should use the StructField type. Building a schema from pyspark.sql.types, as here using classes like StructType and StructField, is one of multiple ways

of expressing a schema in Spark. A StructType always contains a list of StructFields (see documentation linked below). So, nesting StructType and StructType as shown in the Question: is

wrong.

The modification date threshold should be specified by a keyword argument like options(modifiedBefore='2029-03-20T05:44:46') and not two consecutive non-keyword arguments as in the original

code block (see documentation linked below).

Spark cannot identify the file format correctly, because either it has to be specified by using the DataFrameReader.format(), as an argument to DataFrameReader.load(), or directly by calling, for

example, DataFrameReader.parquet().

Columns in the schema are unable to handle empty values and the modification date threshold is specified incorrectly.

No. If StructField would be used for the columns instead of StructType (see above), the third argument specified whether the column is nullable. The original schema shows that columns should be

nullable and this is specified correctly by the third argument being True in the schema in the code block.

It is correct, however, that the modification date threshold is specified incorrectly (see above).

The attributes array is specified incorrectly, Spark cannot identify the file format, and the syntax of the call to Spark's DataFrameReader is incorrect.

Wrong. The attributes array is specified correctly, following the syntax for ArrayType (see linked documentation below). That Spark cannot identify the file format is correct, see correct answer

above. In addition, the DataFrameReader is called correctly through the SparkSession spark.

Columns in the schema definition use the wrong object type and the syntax of the call to Spark's DataFrameReader is incorrect.

Incorrect, the object types in the schema definition are correct and syntax of the call to Spark's DataFrameReader is correct.

The data type of the schema is incompatible with the schema() operator and the modification date threshold is specified incorrectly.

False. The data type of the schema is StructType and an accepted data type for the DataFrameReader.schema() method. It is correct however that the modification date threshold is specified

incorrectly (see correct answer above).

Answer : B

transactionsDf.where(transactionsDf.storeId!=25)

Correct. DataFrame.where() is an alias for the DataFrame.filter() method. Using this method, it is straightforward to filter out rows that do not have value 25 in column storeId.

transactionsDf.select(transactionsDf.storeId!=25)

Wrong. The select operator allows you to build DataFrames column-wise, but when using it as shown, it does not filter out rows.

transactionsDf.filter(transactionsDf.storeId==25)

Incorrect. Although the filter expression works for filtering rows, the == in the filtering condition is inappropriate. It should be != instead.

transactionsDf.drop(transactionsDf.storeId==25)

No. DataFrame.drop() is used to remove specific columns, but not rows, from the DataFrame.

transactionsDf.remove(transactionsDf.storeId==25)

False. There is no DataFrame.remove() operator in PySpark.

More info: pyspark.sql.DataFrame.where --- PySpark 3.1.2 documentation

Static notebook | Dynamic notebook: See test 3, Question: 48 (Databricks import instructions)

Answer : C

This Question: is pretty complex and, in its complexity, is probably above what you would encounter in the exam. However, reading the Question: carefully, you can use your logic skills

to weed out the

wrong answers here.

First, you should examine the join statement which is common to all answers. The first argument of the join() operator (documentation linked below) is the DataFrame to be joined with. Where join is

in gap 3, the first argument of gap 4 should therefore be another DataFrame. For none of the questions where join is in the third gap, this is the case. So you can immediately discard two answers.

For all other answers, join is in gap 1, followed by .(itemsDf, according to the code block. Given how the join() operator is called, there are now three remaining candidates.

Looking further at the join() statement, the second argument (on=) expects 'a string for the join column name, a list of column names, a join expression (Column), or a list of Columns', according to

the documentation. As one answer option includes a list of join expressions (transactionsDf.productId==itemsDf.itemId, transactionsDf.storeId!=itemsDf.itemId) which is unsupported according to the

documentation, we can discard that answer, leaving us with two remaining candidates.

Both candidates have valid syntax, but only one of them fulfills the condition in the Question: 'only where column storeId of DataFrame transactionsDf does not match column itemId of

DataFrame

itemsDf'. So, this one remaining answer option has to be the correct one!

As you can see, although sometimes overwhelming at first, even more complex questions can be figured out by rigorously applying the knowledge you can gain from the documentation during the

exam.

More info: pyspark.sql.DataFrame.join --- PySpark 3.1.2 documentation

Static notebook | Dynamic notebook: See test 3, Question: 47 (Databricks import instructions)

Answer : E

The DataFrame.summary() command is very practical for quickly calculating statistics of a DataFrame. You need to call .show() to display the results of the calculation. By default, the command

calculates various statistics (see documentation linked below), including standard deviation and minimum. Note that the answer that lists many options in the summary() parentheses does not

include the minimum, which is asked for in the question.

Answer options that include agg() do not work here as shown, since DataFrame.agg() expects more complex, column-specific instructions on how to aggregate values.

More info:

- pyspark.sql.DataFrame.summary --- PySpark 3.1.2 documentation

- pyspark.sql.DataFrame.agg --- PySpark 3.1.2 documentation

Static notebook | Dynamic notebook: See test 3, Question: 46 (Databricks import instructions)

Answer : E

Correct code block:

transactionsDfMonday.unionByName(transactionsDfTuesday, True)

Output of correct code block:

+-------------+---------+-----+-------+---------+----+

|transactionId|predError|value|storeId|productId| f|

+-------------+---------+-----+-------+---------+----+

| 5| null| null| null| 2|null|

| 6| 3| 2| 25| 2|null|

| 1| null| 4| 25| 1|null|

| 2| null| 7| 2| 2|null|

| 4| null| null| 3| 2|null|

| 5| null| null| null| 2|null|

+-------------+---------+-----+-------+---------+----+

For solving this question, you should be aware of the difference between the DataFrame.union() and DataFrame.unionByName() methods. The first one matches columns independent of their

names, just by their order. The second one matches columns by their name (which is asked for in the question). It also has a useful optional argument, allowMissingColumns. This allows you to

merge DataFrames that have different columns - just like in this example.

sc stands for SparkContext and is automatically provided when executing code on Databricks. While sc.union() allows you to join RDDs, it is not the right choice for joining DataFrames. A hint away

from sc.union() is given where the Question: talks about joining 'into a new DataFrame'.

concat is a method in pyspark.sql.functions. It is great for consolidating values from different columns, but has no place when trying to join rows of multiple DataFrames.

Finally, the join method is a contender here. However, the default join defined for that method is an inner join which does not get us closer to the goal to match the two DataFrames as instructed,

especially given that with the default arguments we cannot define a join condition.

More info:

- pyspark.sql.DataFrame.unionByName --- PySpark 3.1.2 documentation

- pyspark.SparkContext.union --- PySpark 3.1.2 documentation

- pyspark.sql.functions.concat --- PySpark 3.1.2 documentation

Static notebook | Dynamic notebook: See test 3, Question: 45 (Databricks import instructions)