# Calculate percentages with Flux

Calculating percentages from queried data is a common use case for time series data. To calculate a percentage in Flux, operands must be in each row. Use `map()` to re-map values in the row and calculate a percentage.

To calculate percentages

1. Use `from()`, `range()` and `filter()` to query operands.
2. Use `pivot()` or `join()` to align operand values into rows.
3. Use `map()` to divide the numerator operand value by the denominator operand value and multiply by 100.

The following examples use `pivot()` to align operands into rows because `pivot()` works in most cases and is more performant than `join()`. See Pivot vs join.

``````from(bucket: "example-bucket")
|> range(start: -1h)
|> filter(fn: (r) => r._measurement == "m1" and r._field =~ /field[1-2]/ )
|> pivot(rowKey:["_time"], columnKey: ["_field"], valueColumn: "_value")
|> map(fn: (r) => ({ r with _value: r.field1 / r.field2 * 100.0 }))
``````

## GPU monitoring example

The following example queries data from the gpu-monitor bucket and calculates the percentage of GPU memory used over time. Data includes the following:

• `gpu` measurement
• `mem_used` field: used GPU memory in bytes
• `mem_total` field: total GPU memory in bytes

### Query mem_used and mem_total fields

``````from(bucket: "gpu-monitor")
|> range(start: 2020-01-01T00:00:00Z)
|> filter(fn: (r) => r._measurement == "gpu" and r._field =~ /mem_/)
``````
###### Returns the following stream of tables:
_time_measurement_field_value
2020-01-01T00:00:00Zgpumem_used2517924577
2020-01-01T00:00:10Zgpumem_used2695091978
2020-01-01T00:00:20Zgpumem_used2576980377
2020-01-01T00:00:30Zgpumem_used3006477107
2020-01-01T00:00:40Zgpumem_used3543348019
2020-01-01T00:00:50Zgpumem_used4402341478

_time_measurement_field_value
2020-01-01T00:00:00Zgpumem_total8589934592
2020-01-01T00:00:10Zgpumem_total8589934592
2020-01-01T00:00:20Zgpumem_total8589934592
2020-01-01T00:00:30Zgpumem_total8589934592
2020-01-01T00:00:40Zgpumem_total8589934592
2020-01-01T00:00:50Zgpumem_total8589934592

### Pivot fields into columns

Use `pivot()` to pivot the `mem_used` and `mem_total` fields into columns. Output includes `mem_used` and `mem_total` columns with values for each corresponding `_time`.

``````// ...
|> pivot(rowKey:["_time"], columnKey: ["_field"], valueColumn: "_value")
``````
###### Returns the following:
_time_measurementmem_usedmem_total
2020-01-01T00:00:00Zgpu25179245778589934592
2020-01-01T00:00:10Zgpu26950919788589934592
2020-01-01T00:00:20Zgpu25769803778589934592
2020-01-01T00:00:30Zgpu30064771078589934592
2020-01-01T00:00:40Zgpu35433480198589934592
2020-01-01T00:00:50Zgpu44023414788589934592

### Map new values

Each row now contains the values necessary to calculate a percentage. Use `map()` to re-map values in each row. Divide `mem_used` by `mem_total` and multiply by 100 to return the percentage.

To return a precise float percentage value that includes decimal points, the example below casts integer field values to floats and multiplies by a float value (`100.0`).

``````// ...
|> map(
fn: (r) => ({
_time: r._time,
_measurement: r._measurement,
_field: "mem_used_percent",
_value: float(v: r.mem_used) / float(v: r.mem_total) * 100.0
}),
)
``````
##### Query results:
_time_measurement_field_value
2020-01-01T00:00:00Zgpumem_used_percent29.31
2020-01-01T00:00:10Zgpumem_used_percent31.37
2020-01-01T00:00:20Zgpumem_used_percent30.00
2020-01-01T00:00:30Zgpumem_used_percent35.00
2020-01-01T00:00:40Zgpumem_used_percent41.25
2020-01-01T00:00:50Zgpumem_used_percent51.25

### Full query

``````from(bucket: "gpu-monitor")
|> range(start: 2020-01-01T00:00:00Z)
|> filter(fn: (r) => r._measurement == "gpu" and r._field =~ /mem_/ )
|> pivot(rowKey:["_time"], columnKey: ["_field"], valueColumn: "_value")
|> map(
fn: (r) => ({
_time: r._time,
_measurement: r._measurement,
_field: "mem_used_percent",
_value: float(v: r.mem_used) / float(v: r.mem_total) * 100.0
}),
)
``````

## Examples

#### Calculate percentages using multiple fields

``````from(bucket: "example-bucket")
|> range(start: -1h)
|> filter(fn: (r) => r._measurement == "example-measurement")
|> filter(fn: (r) => r._field == "used_system" or r._field == "used_user" or r._field == "total")
|> pivot(rowKey: ["_time"], columnKey: ["_field"], valueColumn: "_value")
|> map(
fn: (r) => ({
r with _value: float(v: r.used_system + r.used_user) / float(v: r.total) * 100.0
}),
)
``````

#### Calculate percentages using multiple measurements

1. Ensure measurements are in the same bucket.
2. Use `filter()` to include data from both measurements.
3. Use `group()` to ungroup data and return a single table.
4. Use `pivot()` to pivot fields into columns.
5. Use `map()` to re-map rows and perform the percentage calculation.
``````from(bucket: "example-bucket")
|> range(start: -1h)
|> filter(fn: (r) => (r._measurement == "m1" or r._measurement == "m2") and (r._field == "field1" or r._field == "field2"))
|> group()
|> pivot(rowKey: ["_time"], columnKey: ["_field"], valueColumn: "_value")
|> map(fn: (r) => ({r with _value: r.field1 / r.field2 * 100.0}))
``````

#### Calculate percentages using multiple data sources

``````import "sql"
import "influxdata/influxdb/secrets"

pgUser = secrets.get(key: "POSTGRES_USER")
pgPass = secrets.get(key: "POSTGRES_PASSWORD")
pgHost = secrets.get(key: "POSTGRES_HOST")

t1 = sql.from(
driverName: "postgres",
dataSourceName: "postgresql://\${pgUser}:\${pgPass}@\${pgHost}",
query: "SELECT id, name, available FROM example_table",
)

t2 = from(bucket: "example-bucket")
|> range(start: -1h)
|> filter(fn: (r) => r._measurement == "example-measurement" and r._field == "example-field")

join(tables: {t1: t1, t2: t2}, on: ["id"])
|> map(fn: (r) => ({r with _value: r._value_t2 / r.available_t1 * 100.0}))
``````

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