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Tutorial: Purchase Filtering

We will build a simple Purchase Filtering app to showcase some common Quix Streams dataframe-like operations with dictionary/JSON data (a format frequently used).

You'll learn how to:

  • Create a topic
  • Assign a value to a new column
  • Use SDF.apply() with additional operations
  • Filter with inequalities combined with and/or (&, |)
  • Get a subset/selection of columns
  • Produce resulting output to a topic

Outline of the Problem

Imagine we are a company who sells goods to members only: they can have a "Bronze", "Silver", or "Gold" membership.

We always send a coupon to our Silver and Gold members who spend at least $100 in one visit.

We need an application that will filter for the applicable customers and send only the necessary information downstream.

Our Example

We will use a simple producer to generate some mock purchase data to be processed by our new Purchase Filtering application.

Important Takeaways

The primary lesson: learning how you can use common pandas-like operations on dictionary/JSON data to perform various transformations as if it were a dataframe.

Before Getting Started

  • You will see links scattered throughout this tutorial.

    • Tutorial code links are marked >>> LIKE THIS <<< .
    • All other links provided are completely optional.
    • They are great ways to learn more about various concepts if you need it!
  • We use the word "column" for consistency with Pandas terminology.

  • You can also think of it as a dictionary key.

Generating Purchase Data

We have a simple >>> Purchases Producer <<< that generates a small static set of "purchases", which are simply dictionaries with various info about what was purchased by a customer during their visit. The data is keyed on customer ID.

An outgoing Kafka message looks something like:

# ...
kafka_key: "CUSTOMER_ID_123"
        "First Name": "Jane",
        "Last Name": "Doe",
        "Email": "",
        "Membership Type": "Gold",
        "Purchases": [
                "Item ID": "abc123",
                "Price": 13.99,
                "Quantity": 12
                "Item ID": "def456",
                "Price": 12.59,
                "Quantity": 2

Purchase Filtering Application

Now let's go over our >>> Purchase Filtering Application <<< line-by-line!

Create Application

app = Application(
    broker_address=os.environ.get("BROKER_ADDRESS", "localhost:9092"),

First, create the Quix Streams Application, which is our constructor for everything! We provide it our connection settings, consumer group (ideally unique per Application), and where the consumer group should start from on our topic.

NOTE: Once you are more familiar with Kafka, we recommend learning more about auto_offset_reset.

Define Topics

customer_purchases_topic = app.topic(name="customer_purchases")
customers_qualified_topic = app.topic(name="customers_coupon_qualified")

Next we define our input/output topics, named customer_purchases and customers_coupon_qualified, respectively.

They each return Topic objects, used later on.

NOTE: the topics will automatically be created for you in Kafka when you run the application should they not exist.

The StreamingDataFrame (SDF)

sdf = app.dataframe(topic=customer_purchases_topic)

Now for the fun part: building our StreamingDataFrame, often shorthanded to "SDF".

SDF allows manipulating the message value in a dataframe-like fashion using various operations.

After initializing, we continue re-assigning to the same sdf variable as we add operations.

(Also: notice that we pass our input Topic from the previous step to it.)

Filtering Purchases

def get_purchase_totals(items):
    return sum([i["Price"]*i["Quantity"] for i in items])

sdf = sdf[
    (sdf["Purchases"].apply(get_purchase_totals) * SALES_TAX >= 100.00)
    & (sdf["Membership Type"].isin(["Silver", "Gold"]))

We get started with a bang!

Let's break it down step-by-step, as most of our work is done here:

# step A
sdf["Purchases"].apply(get_purchase_totals) * SALES_TAX >= 100.00

Here, we do an SDF.apply(F) operation on a column (F should take your current message value as an argument, and return your new message value): our F here is get_purchase_totals.

Notice how you can still do basic operations with an SDF.apply() result, like multiplying it by our sales tax, and then finally doing an inequality check on the total (all of which are SDF operations...more on that in a second).

# step B
sdf["Membership Type"].isin(["Silver", "Gold"])

We additionally showcase one of our built-in column operations .isin(), a way for SDF to perform an if x in y check (SDF is declaratively defined, invalidating that approach).

NOTE: some operations (like .isin()) are only available when manipulating a column. - if you're unsure what's possible, autocomplete often covers you! - ADVANCED: complete list of column operations.

# "and" Steps A, B
(A) & (B)
Now we "and" these steps, which translates to your typical A and B (and returns a boolean).

A few notes around & (and):

  • It is considered an SDF operation.

  • You MUST use & for and, | for or

  • Your respective objects (i.e. A, B) must be wrapped in parentheses.

Ultimately, when executed, the result of & will be boolean. This is important for...

# filter with "&" result
sdf = sdf[X]
Ultimately, this is a filtering operation: whenever X is an SDF operation(s) result, it acts like Pandas row filtering.

As such, SDF filtering interprets the SDF operation & boolean result as follows:

  • True -> continue processing this event

  • False -> stop ALL further processing of this event (including produces!)

So, any events that don't satisfy these conditions will be filtered as desired!

Adding a New Column

def get_full_name(customer):
    return f'{customer["First Name"]} {customer["Last Name"]}'

sdf["Full Name"] = sdf.apply(get_full_name)

With filtering done, we now add a new column to the data that we need downstream.

This is basically a functional equivalent of adding a key to a dictionary.

>>> {"Remove Me": "value", "Email": "cool email"}`


>>> {"Remove Me": "value", "Email": "cool email", "Full Name": "cool name"}`

Getting a Column Subset/Selection

sdf = sdf[["Email", "Full Name"]]
We only need a couple fields to send downstream, so this is a convenient way to select only a specific list of columns (AKA dictionary keys) from our data.


>>> {"Remove Me": "value", "Email": "cool email", "Full Name": "cool name", }`


>>> {"Email": "cool email", "Full Name": "cool name"}`

NOTE: you cannot reference nested keys in this way.

Producing the Result

sdf = sdf.to_topic(customers_qualified_topic)

Finally, we produce our non-filtered results downstream via SDF.to_topic(T), where T is our previously defined Topic (not the topic name!).

NOTE: by default, our outgoing Kafka key is persisted from the input message. You can alter it, if needed.

Try it yourself!

1. Run Kafka

First, have a running Kafka cluster.

To conveniently follow along with this tutorial, just run this simple one-liner.

2. Install Quix Streams

In your python environment, run pip install quixstreams

3. Run the Producer and Application

Just call python and python in separate windows.

4. Check out the results!

...but wait, I don't see any message processing output...Is it working???

One thing to keep in mind is that the Quix Streams does not log/print any message processing operations by default.

To get visual outputs around message processing, you can either: - use recommended way of printing/logging stuff - use DEBUG mode via Application(loglevel="DEBUG") - WARNING: you should NOT run your applications in DEBUG mode in production.