InfluxDB for time-series data in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this InfluxDB query?

Given the following InfluxDB query executed on a Raspberry Pi collecting temperature data every minute, what will be the output?

SELECT mean("value") FROM "temperature" WHERE time > now() - 1h GROUP BY time(10m)

Assume the data has consistent temperature readings every minute for the last hour.

A Raw temperature values for every minute in the last hour

B A list of average temperature values for each 10-minute interval in the last hour

C An error because GROUP BY time requires a fill() clause

D A single average temperature value for the entire last hour

💡 Hint

Think about how GROUP BY time() works in InfluxDB queries.

The query groups data into 10-minute buckets and calculates the average temperature for each bucket, so the output is a list of averages per 10-minute interval.

🧠 Conceptual

intermediate

Which InfluxDB data type is best for storing Raspberry Pi CPU temperature?

You want to store the Raspberry Pi CPU temperature readings in InfluxDB. Which data type should you use for the temperature field?

A Float

B Boolean

C String

D Integer

💡 Hint

Temperature values can have decimal points.

CPU temperature readings are decimal numbers, so the float type is best to store precise values.

🔧 Debug

advanced

Why does this InfluxDB write command fail on Raspberry Pi?

Consider this Python code snippet trying to write a temperature point to InfluxDB:

from influxdb_client import InfluxDBClient, Point
client = InfluxDBClient(url="http://localhost:8086", token="my-token", org="my-org")
write_api = client.write_api()
point = Point("temperature").tag("device", "raspberry_pi").field("value", "45.3")
write_api.write(bucket="sensors", record=point)

It raises a type error. What is the cause?

A The bucket name "sensors" does not exist

B The tag key "device" is invalid

C The field value is a string instead of a float

D The client URL is incorrect

💡 Hint

Check the data type passed to the field method.

The field method expects a numeric type for measurement values. Passing a string causes a type error.

📝 Syntax

advanced

Which InfluxDB Flux query correctly calculates max temperature per hour?

Choose the correct Flux query to get the maximum temperature per hour from the "temperature" measurement.

A from(bucket: "sensors") |> range(start: -24h) |> filter(fn: (r) => r._measurement == "temperature") |> aggregateWindow(every: 1h, fn: max)

B from(bucket: "sensors") |> range(start: -24h) |> filter(fn: (r) => r._measurement == "temperature") |> window(every: 1h) |> max()

C from(bucket: "sensors") |> range(start: -24h) |> filter(fn: (r) => r._measurement == "temperature") |> max(every: 1h)

D from(bucket: "sensors") |> range(start: -24h) |> filter(fn: (r) => r._measurement == "temperature") |> aggregateWindow(every: 1h, fn: mean)

💡 Hint

aggregateWindow is used to group data by time intervals and apply aggregation.

Option A correctly uses aggregateWindow with max function to get max temperature per hour.

🚀 Application

expert

How many points are stored after this batch write?

You run this Python code on your Raspberry Pi to write temperature data points to InfluxDB:

from influxdb_client import InfluxDBClient, Point
client = InfluxDBClient(url="http://localhost:8086", token="token", org="org")
write_api = client.write_api()
data = [
  Point("temperature").field("value", 20.1).tag("device", "pi1"),
  Point("temperature").field("value", 21.3).tag("device", "pi2"),
  Point("temperature").field("value", 19.8).tag("device", "pi1"),
  Point("humidity").field("value", 55).tag("device", "pi1")
]
write_api.write(bucket="sensors", record=data)

How many points are stored in the "sensors" bucket?

A 1 point

B 3 points

C 2 points

D 4 points

💡 Hint

Each Point object represents one data point.

There are 4 Point objects in the list, so 4 points are written to the bucket.