Skip to content

relationalai.std.math.log()

log(x: Number|Producer, base: Number|Producer|None = None) -> Expression

Calculates the logarithm of x with the specified base. If base is None, the natural logarithm (base e) is used. If x or base is a Producer, log() filters out any non-numeric or negative values from the producer. Must be called in a rule or query context.

Parameters

Name	Type	Description
`x`	`Producer` or Python `Number` object	The number to take the logarithm of.
`base`	`Producer` or Python `Number` object or `None`	The base of the logarithm. If `None`, the natural logarithm (base `e`) is used.

Returns

An Expression object.

Example

Use log() to calculate the logarithm of a number with a specified base:

import relationalai as rai
from relationalai.std import math


# =====
# SETUP
# =====

model = rai.Model("MyModel")
Person = model.Type("Person")

with model.rule():
    Person.add(id=1).set(name="Alice", age=9)
    Person.add(id=2).set(name="Bob", age=-10)  # Negative age
    Person.add(id=3).set(name="Carol", age="INVALID")  # Non-numeric age


# =======
# EXAMPLE
# =======

# Set age_log and age_log2 properties to the natural and base-2 logarithms of
# each person’s age.
with model.rule():
    person = Person()
    person.set(age_log=math.log(person.age))
    person.set(age_log2=math.log(person.age, base=2))

# Since log() filters out negative and non-numeric values, the age_log and
# age_log2 properties are not set for Bob or Carol.
with model.query() as select:
    person = Person()
    response = select(person.id, person.name, person.age_log2)

print(response.results)
#    id     name  age_log2
# 0   1    Alice  3.169925
# 1   2      Bob       NaN
# 2   3    Carol       NaN

See Also