Expression Translator (EXTRA)

To access this screen:

• Run the EXTRA process from the command line by typing 'extra'. Specify an input file, output file and (optionally) retrieval criteria and click OK - the Expression Translator displays.

For more information on the EXTRA process, see EXTRA.

EXTRA Key Concepts

Transform

EXTRA applies a “transform” to the contents of a file. It does this through one or more “statements”.

Statements

A transform consists of multiple statements. Statements are separated by spaces or new-lines. There are three kinds of statements

Assignment statements

Assignment statements evaluate an expression and assign the result to a field.

“IF” statements

“If” statements use the value of one or more expressions to execute other statements conditionally.

Procedure statements

Procedure statements do something but do not return a value. Some procedures (”erase”, “keep”, “saveonly”) require a list of field names (not expressions). The other procedures (”delete”, “exit”) don’t require any other information.

Expressions

Expressions are used in assignment and “If” statements. There are 4 types.

Simple expressions

A simple expression is a number, text string or field reference.

Arithmetic expressions

The value of an arithmetic expression is the result of applying the arithmetic operator (+, -, * or /) to the expressions on the left and right of the operator.

Relational expressions

The value of a relational expression, like “X < 2”, is 1.0 if the expression is “true” and 0.0 if it is “false”. They may be used anywhere an arithmetic expression may be used.

Function expressions

A function expression takes zero or more expressions in brackets to calculate a new value. For example, the value of “min(X, 2)” is the smaller of the values of the two expressions “X” and “2”.

Entering Expressions

Logical expressions can be entered using either (or both) of the following methods:

• Type the expression you want directly into the Expression field.

• Construct an expression by selecting various parameter components, such as field names, operations, functions and procedures.

For examples and further guidance on using expressions in Studio products, see  .

To define a logical expression for the EXTRA process:

1. Enter all or part of a logical expression into the Transform field.

2. To add preformatted text to the current cursor position (in the Transform field):

   • Add one or more Input Fields to the transform using the list provided. The fields are derived from the IN file of the EXTRA process.

   • Add one of the Operators to the expression using the buttons provided:

     ==	equal to
     !=	not equal to
     <	less than
     <=	less than or equal to
     >	greater than
     >=	greater than or equal to

3. Choose one of the Functions and Procedures, categorized into Numeric Functions, String Functions, Logic Constructs, Procedures and Record Selection functions:

   • Numeric Functions are used to perform mathematical functions on explicit or data-stored values, including:

     Function name	Arguments	Returns
     abs	X	The absolute (positive) value of X
     absent	none	The Datamine "absent data" value
     acos	X	The angle whose cosine is X
     asin	X	The angle whose sine is X
     atan	X	The angle whose tangent is X
     atan2	X	A two-argument arctangent function. It calculates the angle ( \theta ) between the positive x-axis and the point ((x, y)) in the Cartesian plane. This angle is measured in radians and ranges from (-\pi) to (\pi) 12. See EXTRA examples.
     azimuth	X	The azimuth in degrees of a line from (0, 0) to (dx, dy). See EXTRA examples.
     cos	X	The cosine of X
     decode	X	The numeric value of the first set of numeric characters embedded in X
     default	X	The default value of X
     exp	X	The constant "e" raised to the power of X
     ijkget	X,X	Returns values encoded into the block model index. See EXTRA examples.
     ijknum	I,J,K	Combines separate I, J and K indexes into a single IJK index
     int	X	The integer part of X
     len	A	The length (up to the first trailing space) of A
     log	X	The base-10 logarithm of X
     loge, logn	X	The base-"e" logarithm of X
     match	A, P	The position where a regular expression P matches characters in A
     max	X1, X2, X3, ...	The maximum value of X1, X2, X3, ...
     maxia	X1, X2, X3, ...	The maximum value of X1, X2, X3, ... ignoring absent arguments.
     min	X1, X2, X3, ...	The minimum value of X1, X2, X3, ... ignoring absent arguments. For example: minia(absent(), 100, 2) = 2 min(absent(), 100, 2) = absent)
     minia	X1, X2, X3, ...	The minimum value of X1, X2, X3, ...
     mod, modc	X, Y	The remainder when X is divided by Y
     phi	X	The inverse normal distribution function
     pow, rais	X, Y	The value of X raised to the power of Y
     round	X, Y	Round off the value X to the nearest multiple of Y.  Equivalent to Y*int(X/Y + 0.5)
     sin	X	The sine of X
     special	X	One of your application's "special" values.
     sqrt	X	The square root of X
     tan	X	The tangent of X
     xyzijk	X,X,X	Creates an IJK index number from X, Y and Z model coordinates. See EXTRA examples

   • String Functions can be applied to alphanumeric values, including:

     Function name	Arguments	Returns
     concat	A1,A2	The concatenation of the alphanumeric values A1, A2.
     default	X	The default value of X
     field	F1	The contents of a field. The field name must be supplied as a string - for example, field ("AU"). This allows field names with otherwise prohibited characters, such as  '-', to be referenced. This function can only be used for getting the value of a field - not for setting it.
     join	A1, A2, A3, ...	The concatenation of the alphanumeric values A1, A2, A3, ...
     lcase	A	Returns the string given as an argument, with all upper case letters converted to lower case
     string	N, M	The numeric value N, converted to a string with M decimals. If M is omitted, the function uses a general-purpose numeric format.
     substr	A, N, M	Returns a sub-string, consisting of M characters taken from A, starting with character N. If M is omitted, all characters from N to the end are returned.
     trim	A	Returns the value of A with trailing spaces removed
     type	A	Returns a string of characters that describe the type of the field. See EXTRA examples
     ucase	A	Returns the string given as an argument, with all lower case letters converted to upper case

   • Proceduresunlike functions, don't return a value. They just carry out an action. EXTRA provides the following procedures:

     Procedure	Arguments	Description
     delete	none	Deletes the current record
     erase	F1, F2, F3, ...	Erases the fields F1, F2, F3, ... from the output file
     exit	none	Immediately terminate processing before the current record has been written. See EXTRA examples.
     keep	F1, F2, F3, ...	Define the fields that will be in the output file. See EXTRA examples.
     saveonly	F1, F2, F3, ...	Erases all fields except F1, F2, F3, ... from the output file. If used more than once, only the values in the last saveonly are honoured. See EXTRA examples.

   • Logic Constructscreate conditional statements using the following options:

     Procedure	Arguments	Description
     if() end	Condition	If the condition filter passes, functions before the next end are performed, if possible.
     if() else end	Condition	If the condition filter passes, functions before the next else are performed, otherwise the instructions between else and end are performed.
     if() elseif end	Condition	Similar to if() else but evaluate against multiple conditions. IF-ELSEIF-END type statements are efficient as EXTRA only needs to evaluate the condition once (as opposed to multiple times if multiple IF-END statements are used). For example: IF(SLPCODE==0) SLOPE=0 ELSEIF(SLPCODE==1) SLOPE=50 ELSEIF(SLPCODE==99) SLOPE=33 END
     if() elseif else end	Condition	An extension of if() elseif end. If data does not match any previous elseif condition, the logic after else (and before end) is executed if possible.
     not()	Condition	Used typically as part of an if() type statement to exclude passing conditions. For example: IF(SLPCODE==0)NOT(SLPCODE==999) SLOPE=1000 END If the argument is zero, it returns 1.0, otherwise it returns 0.0. So, to invert the statement if (X > 1 and Y < 0) ... You could use: if (X <= 1 or Y >= 0) ... ...or simply: if (not( X > 1 and Y < 0) ) ...

     
     For all of the above, see EXTRA examples.

   • Record Selection functions allow you to navigate throughout the specified IN database. They include:

     Function name	Arguments	Returns
     first	none	If processing the first record, returns 1.0, otherwise returns 0.0
     last	none	If processing the last record, returns 1.0, otherwise returns 0.0
     prev	X	The value of field X from the previous record
     next	X	The value of field X from the next record

4. Click the respective Add button to transfer preformatted text to the Expression field.

5. Test the validity of your expression. You are told if the expression is valid ("OK") or not.

   If a syntax error occurs, the Status field indicates which line is problematic.

   Note: to restart your expression, use Clear. You can't undo this.

6. Execute your expression using the EXTRA process.

Related topics and activities

• EXTRA (process)

• EXTRA examples