stddev()

Calculates the population standard deviation of numeric values returned by an expression.

Syntax

stddev(NUM_EXPR)

Parameters

NUM_EXPR: An expression that returns the numeric values for which to calculate the standard deviation.

Description

The stddev() function internally computes the square root of var(NUM_EXPR). Because it is based on the population variance (divided by N), it returns the population standard deviation. Null values and non-numeric values are ignored. If there are no values, it returns null. If there is exactly one value, it returns 0.0. The return value is a 64-bit floating-point number (double).

Use this function in aggregation commands such as stats and timechart.

Error codes

Code	Description
91020	The number of arguments is incorrect.

Usage examples

To prepare the WEB_APACHE_SAMPLE table used in these examples, refer to Preparing sample data.

Calculate the standard deviation of response sizes across all requests
```
table WEB_APACHE_SAMPLE | stats stddev(bytes)
```
Calculate the standard deviation of response sizes per HTTP method
```
table WEB_APACHE_SAMPLE | stats stddev(bytes) by method
```

Null value handling

json "[{'val': 10}, {'val': null}, {'val': 30}]"
| stats stddev(val)
| # Null values are ignored.

Compatibility

The stddev() function has been available since before Logpresso Sonar 4.0.