Databricks Databricks-Certified-Associate-Developer-for-Apache-Spark-3.0 Exam With Confidence Using Practice Dumps

Explanation

Correct code block:

def count_to_target(target):

if target is None:

return

result = list(range(target))

return result

count_to_target_udf = udf(count_to_target, ArrayType(IntegerType()))

transactionsDf.select(count_to_target_udf('predError'))

Output of correct code block:

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

|count_to_target(predError)|

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

| [0, 1, 2]|

| [0, 1, 2, 3, 4, 5]|

| [0, 1, 2]|

| null|

| null|

| [0, 1, 2]|

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

This QUESTION NO: is not exactly easy. You need to be familiar with the syntax around UDFs (user-defined functions). Specifically, in this QUESTION NO: it is important to pass the correct types

to the udf

method - returning an array of a specific type rather than just a single type means you need to think harder about type implications than usual.

Remember that in Spark, you always pass types in an instantiated way like ArrayType(IntegerType()), not like ArrayType(IntegerType). The parentheses () are the key here - make sure you do not

forget those.

You should also pay attention that you actually pass the UDF count_to_target_udf, and not the Python method count_to_target to the select() operator.

Finally, null values are always a tricky case with UDFs. So, take care that the code can handle them correctly.

More info: How to Turn Python Functions into PySpark Functions (UDF) – Chang Hsin Lee – Committing my thoughts to words.

Static notebook | Dynamic notebook: See test 3, QUESTION NO: 24 (Databricks import instructions)

Explanation

Output of correct code block:

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

|itemName |col |

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

|Thick Coat for Walking in the Snow|blue |

|Thick Coat for Walking in the Snow|winter|

|Thick Coat for Walking in the Snow|cozy |

|Outdoors Backpack |green |

|Outdoors Backpack |summer|

|Outdoors Backpack |travel|

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

The key to solving this QUESTION NO: is knowing about Spark's explode operator. Using this operator, you can extract values from arrays into single rows. The following guidance steps through

the

answers systematically from the first to the last gap. Note that there are many ways to solving the gap questions and filtering out wrong answers, you do not always have to start filtering out from the

first gap, but can also exclude some answers based on obvious problems you see with them.

The answers to the first gap present you with two options: filter and where. These two are actually synonyms in PySpark, so using either of those is fine. The answer options to this gap therefore do

not help us in selecting the right answer.

The second gap is more interesting. One answer option includes "Sports".isin(col("Supplier")). This construct does not work, since Python's string does not have an isin method. Another option

contains col(supplier). Here, Python will try to interpret supplier as a variable. We have not set this variable, so this is not a viable answer. Then, you are left with answers options that include col

("supplier").contains("Sports") and col("supplier").isin("Sports"). The QUESTION NO: states that we are looking for suppliers whose name includes Sports, so we have to go for the contains operator

here.

We would use the isin operator if we wanted to filter out for supplier names that match any entries in a list of supplier names.

Finally, we are left with two answers that fill the third gap both with "itemName" and the fourth gap either with explode("attributes") or "attributes". While both are correct Spark syntax, only explode

("attributes") will help us achieve our goal. Specifically, the QUESTION NO: asks for one attribute from column attributes per row - this is what the explode() operator does.

One answer option also includes array_explode() which is not a valid operator in PySpark.

More info: pyspark.sql.functions.explode — PySpark 3.1.2 documentation

Static notebook | Dynamic notebook: See test 3, QUESTION NO: 39 (Databricks import instructions)

Explanation

Correct code block:

transactionsDf.join(broadcast(itemsDf), "transactionId", "left_semi")

This QUESTION NO: is extremely difficult and exceeds the difficulty of questions in the exam by far.

A first indication of what is asked from you here is the remark that "the query should be executed in an optimized way". You also have qualitative information about the size of itemsDf and

transactionsDf. Given that itemsDf is "very small" and that the execution should be optimized, you should consider instructing Spark to perform a broadcast join, broadcasting the "very small"

DataFrame itemsDf to all executors. You can explicitly suggest this to Spark via wrapping itemsDf into a broadcast() operator. One answer option does not include this operator, so you can disregard

it. Another answer option wraps the broadcast() operator around transactionsDf - the bigger of the two DataFrames. This answer option does not make sense in the optimization context and can

likewise be disregarded.

When thinking about the broadcast() operator, you may also remember that it is a method of pyspark.sql.functions. One answer option, however, resolves to itemsDf.broadcast([...]). The DataFrame

class has no broadcast() method, so this answer option can be eliminated as well.

All two remaining answer options resolve to transactionsDf.join([...]) in the first 2 gaps, so you will have to figure out the details of the join now. You can pick between an outer and a left semi join. An

outer join would include columns from both DataFrames, where a left semi join only includes columns from the "left" table, here transactionsDf, just as asked for by the question. So, the correct

answer is the one that uses the left_semi join.