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Use the log2 function in APL to compute the base-2 logarithm of a positive numeric value. The function is the inverse of exp2. log2 is useful when working with data measured on a binary scale, such as memory sizes, network packet lengths, or binary tree structures. Because each unit increase in log2(x) corresponds to a doubling of x, log2 is a natural choice for analyzing values that grow or shrink by factors of two. You can also use it to compute geometric means in base-2 space.

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For users of other query languages

If you come from other query languages, this section explains how to adjust your existing queries to achieve the same results in APL.
Splunk SPL doesn’t include a built-in log2() function. You compute it as ln(x) / ln(2) or log(x) / log(2).
| eval log2_duration = ln(req_duration_ms) / ln(2)
Standard SQL does not define a LOG2() function. In SQL Server you compute it as LOG(x) / LOG(2). PostgreSQL offers LOG(2, x) for base-2 logarithms.
SELECT LOG(req_duration_ms) / LOG(2) AS log2_duration FROM logs

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Usage

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Syntax

log2(x)

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Parameters

NameTypeRequiredDescription
xrealYesA positive real number (x > 0).

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Returns

  • The base-2 logarithm of x.
  • null if x is negative, zero, or cannot be converted to a real value.

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Example

Use log2 to express request durations on a binary log scale where each unit represents a doubling. Query 
['sample-http-logs']
| where req_duration_ms > 0
| extend log2_duration = log2(req_duration_ms)
| project _time, id, req_duration_ms, log2_duration
Run in Playground Output
_timeidreq_duration_mslog2_duration
2024-11-14 10:00:00user-11.00.000
2024-11-14 10:01:00user-264.06.000
2024-11-14 10:02:00user-31024.010.000
  • exp2: Returns 2^x. Use it as the inverse of log2.
  • log: Returns the natural logarithm. Use it when you prefer the natural base rather than base-2.
  • log10: Returns the base-10 logarithm. Use it for order-of-magnitude analysis instead of binary analysis.
  • pow: Raises a value to a power. Use it to compute powers of two directly as an alternative to exp2.
  • round: Rounds a value. Use it after log2 to bucket data into binary power groups.