Overview

When writing expressions and scripts in PhixFlow, you can use different types of variable.

Attribute names are like the column headings in a spreadsheet.
- You can reference an attribute using its name in other attributes, expressions and file collectors.
- In expressions, attribute names can be qualified with pipe names like this: <pipename>.<attributename> for example in.recordID.
- Database collectors are a special case. They generate implicit attribute names from the names of the fields returned by the database query.
Internal Variables are created and populated by PhixFlow when certain actions happen.
For example, when you load data via a file collector, the stream automatically includes the attribute _fileName to indicate the original file.
User-defined variables are the variables you can create to hold data required for complex calculations in attributes or other expressions. These are prefixed with a $ character, so are called $-variables.

Sections on this page

This page summarises which variables are available in different contexts, and explains how to create and use $-variables. See also Expression Basics.

The following tables gives some guidelines for the availability of variables, based on the PhixFlow Timing Cycle for evaluating analysis models.

Location of Expression	Available Variables
Input multiplier	Some internal variables e.g. _toDate $-variables declared locally in the input multiplier
Database collector SQL script	_inputMultiplier %USERNAME%, %PASSWORD% $-variables
Output Multiplier	internal variables e.g. _toDate $-variables
Attribute expression	internal variables e.g. _toDate All <pipeName> values e.g. inpipe.accountVal All _out.value where value is the name of the attribute and it is before the current attribute in the stream All user defined variables created in a prior attribute expression
Output filter expression	internal variables e.g. _toDate All _out.attribute values All user defined variables created in any Attribute expression
Pipe index expression on a lookup pipe	internal variables <pipename>.attribute - the name on an input pipe All _out.value where value is the name of the attribute and it is before the current attribute in the stream

Variable Scoping

When writing expressions that reference variables it is important to understand whether PhixFlow has "seen" the variable yet. This is the scope of the variable.

In a stream, output multiplier or output filter, the attributes have a specified order. When you run analysis on a model, PhixFlow processes each attribute in order, evaluating their expressions. This means you cannot reference:

an attribute name before PhixFlow has processed it. So in the first attribute in a stream, you cannot use a value from the third attribute in the stream.
a $-variable before PhixFlow has processed the expression where it is set.

You can only reference:

an attribute name in a subsequent attribute
a $-variable after it has been set or evaluated.

Internal Variables

PhixFlow has a list of Internal Variables. For example, some common ways to reference attributes in a stream:

Variable	Syntax	Example
`.`	`<pipe_name>.<attribute_name>`	`in.AppleHarvestDate`	Indicates the source of the attribute is the incoming pipe. The default name for a pipe is "in".
_out	_`out.<attribute_name>`	`_out.AppleHarvestDate`	PhixFlow processes stream attributes in the specified order. Use _`out` indicates an attribute in the same stream that PhixFlow has already processed. If your expression is not working, check to make sure anything it references has already been processed or evaluated by PhixFlow. If the expression is referencing something that will be processed later, PhixFlow will not be able to evaluate the expression.
toDate	see toDate	`if( _out.AppleHarvestDate < _toDate('20210101'), 1, 0)`	In this case one of the arguments in an if statement is an internal variable, that indicates the date up-to which PhixFlow will process a record.

The internal variables that you can use in an expression depend on context. Remember to check the properties page for the item on which you are working; see Property Tabs.

Creating and Using $-variables

Defining a $-variable

Expression Style

All user-defined variables must start with the $ character.
For multi-word variable names, use no spaces and camel case.
It can be useful to know whether a variable is used in other expressions. As there is no way to check this, we recommend using the following naming convention:
To distinguish between $-variables that are:
- only used in the current expression or attribute, use a lowercase first letter, for example $percent.
  These are sometimes called local.
- used in other expressions or attributes, use an uppercase first letter, for example $Percent.These are sometimes called global.

PhixFlow assumes that you are declaring a variable and setting its value the first time it occurs in the expression.

$localVar = 'Smith' $GlobalVar = 'St.John-Smith'

Using $-Variables in Expressions

In expressions that have complex calculations, you may need a variable to hold the result of a calculation. You can then reference the variable later in the expression, or in other attribute expressions for the same stream.

The following expression uses do() function and $-variables for a simple calculation.

Expression Result

do(
$A = 5,
$B = 2,

$A*$B)

This expression

Sets values for 2 $-variables: $A and$ B
Performs simple calculation
Returns 10

do( $c = 10,

$A*$B*$C )

A different expression

Sets another variable value
References the $-variables from the previous expression
Returns 100

When to Use $-variables

$-variables are not really needed in simple calculations. They are useful:

in forEach loops
calculating attibute names from pipes; see Assigning Values From a Pipe.
to store a value from a look-up pipe, when you need the value in multiple attributes
1. In the first attribute, look-up the value.
2. Use a $-variable to store the value that is returned by the look-up.
3. When you need the value in another attribute, reference the $-variable instead of repeating the look-up.
in complex expressions, to break up multiple consecutive functions into separate lines. In this case, use a $-variable to store the intermediate values; see Multiline Statements and $-variables.

Variable Typing

When a variable is first used, PhixFlow makes a best guess about what type of data is stored in that variable; see Parameter Types. For example:

Expression	PhixFlow identifies data type
`$thisNumber = 4`	integer
`$thisAddress = '123 Fake St'`	string

When PhixFlow has decided what type of data is stored in a variable, you usually cannot change the type. PhixFlow will reject an expression that equates different types, such as:

$thisNumber = $thisAddress

The cases where you may be able to change a data type are

integer to a floating point value: PhixFlow may be able to convert between these.
by using type conversion function, such as toDate. This forces a value of one type into a variable of another type.

Using Variables