Flow operators (map, filter, transform) in Kotlin - Mini Project: Build & Apply

Flow operators (map, filter, transform)

📖 Scenario: You are working with a list of numbers representing daily temperatures in Celsius. You want to process this data to find interesting information using Kotlin Flow operators.

🎯 Goal: Build a Kotlin program that uses Flow operators map, filter, and transform to process a flow of temperature data and print the results.

📋 What You'll Learn

Create a flow from a list of temperatures

Use a map operator to convert Celsius to Fahrenheit

Use a filter operator to keep only temperatures above a threshold

Use a transform operator to emit a custom message for each temperature

Collect and print the final results

💡 Why This Matters

🌍 Real World

Processing streams of sensor data or user inputs often requires filtering and transforming data in real time.

💼 Career

Understanding Kotlin Flow operators is important for Android developers and backend engineers working with reactive streams.

1

Create a flow from a list of temperatures

Create a list called temperaturesCelsius with these exact values: 10, 15, 20, 25, 30. Then create a flow called temperatureFlow from this list using asFlow().

Kotlin

# Create the list temperaturesCelsius and the flow temperatureFlow
# Your code here

Need a hint?

Use listOf to create the list and asFlow() to convert it to a flow.

2

Add a threshold variable for filtering

Create an integer variable called thresholdFahrenheit and set it to 68. This will be used to filter temperatures at or above this value in Fahrenheit.

Kotlin

import kotlinx.coroutines.flow.asFlow

val temperaturesCelsius = listOf(10, 15, 20, 25, 30)
val temperatureFlow = temperaturesCelsius.asFlow()

# Create the thresholdFahrenheit variable
# Your code here

Need a hint?

Just create a simple integer variable with the exact name and value.

3

Use map, filter, and transform operators on the flow

Create a new flow called processedFlow by applying these operators on temperatureFlow: first use map to convert Celsius to Fahrenheit using the formula F = C * 9 / 5 + 32, then use filter to keep only temperatures greater than or equal to thresholdFahrenheit, and finally use transform to emit a string message in the format "Temperature: X°F is warm" where X is the temperature in Fahrenheit.

Kotlin

import kotlinx.coroutines.flow.asFlow
import kotlinx.coroutines.flow.map
import kotlinx.coroutines.flow.filter
import kotlinx.coroutines.flow.transform

val temperaturesCelsius = listOf(10, 15, 20, 25, 30)
val temperatureFlow = temperaturesCelsius.asFlow()

val thresholdFahrenheit = 68

# Create processedFlow by applying map, filter, and transform on temperatureFlow
# Your code here

Need a hint?

Chain the operators in this order: map, then filter, then transform. Use emit inside transform to send the message.

4

Collect and print the processed flow results

Use runBlocking to collect the processedFlow and print each emitted string.

Kotlin

import kotlinx.coroutines.runBlocking

# Collect processedFlow and print each message
# Your code here

Need a hint?

Use runBlocking and collect to get the flow values and print them.