Expressions: Overview
The FastStats Expression tool provides multiple functions that allow you to manipulate your data for analysis and/or output purposes.
Expressions are currently used in four places in FastStats:

Calculate Expression wizard to populate a new variable according to a mathematical expression or logical rule

Cube as a cube statistic or dimension

Data Grid as an output column

Like a variable in a Selection
FastStats supports the following in Expressions:

Aggregation Functions  Functions that allow the aggregation of multiple values, such as finding the minimum of a list.

Date Conversion Functions  Functions to support the conversion of dates

Date Functions  Functions allowing the manipulation of date fields.

Date List Functions  Functions used to compare a list of dates

FastStats Variables  Using FastStats variables in expressions

File Functions  Functions used to look up a value or read a column from the file in the path parameter

Inequality Operators  Operators to support comparisons such as 'greater than'.

Location Functions  Geo functions that allow the use of latitude and longitude to calculate distance as well as selecting parts of UK postcodes.

Logical Functions  Functions for building conditional expressions.

Maths Functions  Functions allowing square roots and logs.

Missing Values  Missing value support.

Operators  Simple operations such as addition and subtraction.

Queries  Using queries in expressions

Selector Functions  Functions used to manipulate the codes, descriptions, values or indices of selector functions

String Functions  Functions to support text processing
FastStats also offers the ability to create Aggregated Expressions 'on the fly' and Derived Cube Expressions.
More information and worked examples can also be found in the FS User Guide  Expressions.