#### StdDev

Function

- StdDev(array_variable);
- StdDev(field_variable);
- StdDev(field_variable, groupby);

Description

This function is used to find the standard deviation of a group of values referred to by the first argument. The second argument, if there is one, gives the group by field name.

Arguments

- field_variable
  field_variable is a special variable in Formula, and refers to a group of values from a database or formula field. Whatever kind of source the data comes from, database or formula, it should be of the Number data type.
- array_variable
  array_variable refers to an array whose element should be a Number value.
- groupby
  groupby can be a constant String to indicate the groupby field name, or a field variable on which grouping occurs, or a parameter variable that can accept a different value before each execution of a report.

Return type

Returns a Number value.

Examples

- `Number x = StdDev([1.0, 2.0, 3.0, 4.5, 45.0, 67.0])`
- `Number x[6] = [1.0, 2.0, 3.0, 4.5, 45.0, 67.0];
  Number y = StdDev(x)`
- `Number x = StdDev(@dbfield)`
- `Number x = StdDev(@formula)`
- `Number x = StdDev(@dbfield, "group_field")`
- `Number x = StdDev(@dbfield, @"group_field")`
- `Number x = StdDev(@dbfield, @parameter)`

Note: If a field_variable is assigned to a variable, for example X, the variable X will lose the characteristic of representing a group of values. The following formula will then be treated as incorrect.

`Number x = @dbfield;
Number y = StdDev(x); // system will prompt you that there is no such kind of function.`