Operate on columns

This page documents an earlier version of InfluxDB. InfluxDB v2.7 is the latest stable version. View this page in the v2.7 documentation.

Use the following common queries to operate on columns:

• Find and count unique values in a column
• Recalculate the _values column
• Calculate a new column

These examples use NOAA water sample data.

Find and count unique values in a column

Find and count the number of unique values in a specified column. The following examples find and count unique locations where data was collected.

Find unique values

This query:

• Uses group() to ungroup data and return results in a single table.
• Uses keep() and unique() to return unique values in the specified column.

from(bucket: "noaa")
    |> range(start: -30d)
    |> group()
    |> keep(columns: ["location"])
    |> unique(column: "location")

Example results

Count unique values

This query:

• Uses group() to ungroup data and return results in a single table.
• Uses keep(), unique(), and then count() to count the number of unique values.

from(bucket: "noaa")
    |> group()
    |> unique(column: "location")
    |> count(column: "location")

Example results

Recalculate the _values column

To recalculate the _value column, use the with operator in map() to overwrite the existing _value column.

The following query:

• Uses filter() to filter the average_temperature measurement.
• Uses map() to convert Fahrenheit temperature values into Celsius.

from(bucket: "noaa")
    |> filter(fn: (r) => r._measurement == "average_temperature")
    |> range(start: -30d)
    |> map(fn: (r) => ({r with _value: (float(v: r._value) - 32.0) * 5.0 / 9.0} ))

Calculate a new column

To use values in a row to calculate and add a new column, use map(). This example below converts temperature from Fahrenheit to Celsius and maps the Celsius value to a new celsius column.

The following query:

• Uses filter() to filter the average_temperature measurement.
• Uses map() to create a new column calculated from existing values in each row.

from(bucket: "noaa")
    |> filter(fn: (r) => r._measurement == "average_temperature")
    |> range(start: -30d)
    |> map(fn: (r) => ({r with celsius: (r._value - 32.0) * 5.0 / 9.0}))

Example results

queries