Standard deviation (biased) (stddev)

[ 1 Description ] [ 2 How does it work in the search window? ] [ 3 How does it work in LINQ? ]

Description

This operation calculates the biased standard deviation of the values found in a specified column for each grouping occurrence. If you want to exclude null values, you can use the Non-null standard deviation (biased) (nnstddev) operation and if you want to calculate the unbiased variant, you can use the Standard deviation (unbiased) (ustddev) operation.

How does it work in the search window?

Before being able to perform this operation, you have to group your data. Be aware that the columns used as arguments for the grouping operation will not be available to select as arguments for the aggregation operation.

After grouping the data, select Aggregation in the search window toolbar, then select the Standard deviation (biased) operation. You need to specify one argument:

Argument	Data type

Argument	Data type
Biased standard deviation of ^mandatory	integer, float

The data type of the aggregated values is integer or float.

Example

In the siem.logtrust.web.activity table, we want to calculate the biased standard deviation of the values in the responseLength column during each 5-minute period. Before aggregating the data, the table must be grouped in 5-minute intervals. Then we will perform the aggregation using the Standard deviation (biased) operation.

The arguments needed for the Standard deviation (biased) operation are:

Biased standard deviation of → responseLength column

Click Aggregate function and you will see the following result:

How does it work in LINQ?

Group your data using the following structure:

group every server period by column1, column2...
every client period

Then, use select... as... to add the new column that will show the aggregated values. This is the syntax for the Standard deviation (biased) operation:

stddev(numeric_column)

See Build a query using LINQ to learn more about grouping and aggregating your data using the LINQ language.

Example

You can copy the following LINQ syntax and try the example above on the siem.logtrust.web.activity table:

from siem.logtrust.web.activity
  group every 5m
  every 5m
  select stddev(responseLength) as responseLength_stddev