dataTools

Some useful methods for working with various data types.

infer_data_type

This method accepts a number of 4D objects and attempts to determine what type the content of the object is.

It is particularly useful working with imported data. Let's say you have parsed a text file to a 2D text array and now need to determine what kind of data is in each column. In this example we have a price list that looks like:

We know the arrays are text but what about the values in them?

ARRAY TEXT($aText;0;0)
priceList_array(->$aText)

var $values_c;$temp_c : Collection

$values_c:=New collection()

$temp_c:=New collection()
ARRAY TO COLLECTION($temp_c;$aText{1})
$values_c.push(infer_content_type($temp_c))

ARRAY TO COLLECTION($temp_c;$aText{2})
$values_c.push(infer_content_type($temp_c))

ARRAY TO COLLECTION($temp_c;$aText{3})
$values_c.push(infer_content_type($temp_c))
//  $values_c [ 2, 2, 1 ] or [ Is text, Is text, Is real ]

The data types are inferred by looking down an array and taking a vote on what the dominant data type is. Notice that it correctly identifies the first column which is filled with strings that contain valid number characters and not being the right shape to actually be numbers.

It also works on individual values.

var $value : Variant

$value:="1234568.000"
$this_type:=infer_content_type($value)  //  $this_type = 1

$value:=False
$this_type:=infer_content_type($value)  //  $this_type = 6

$value:=Current date
$this_type:=infer_content_type($value)  //  $this_type = 4

$value:=String($value)
$this_type:=infer_content_type($value)  //  $this_type = 4

Notice the last instance where $value is a text string of the Current date. Why is it still indicated as a date type? Because we are infering the content of $value instead of $value itself.

Take a look at infer_content_type_unitTests for a more complete set of examples.

nvl

nvl is useful for testing individual variables on the fly. You pass a variable to nvl with the expected data type.

• If the variable matches the expected type it returns $1 unchanged.
• If the variable doesn't match it returns Null or a default value you specify. nvl also maps Is undefined to Null. So if you don't specifically need to know the difference between undefined and Null you can make that test in a single call.

The ability to specify the value returned on Null can be very helpful. It's particularly useful for dealing with methods and functions that recieve Variant parameters. For example, let's say you have a method that recieves a variant parameter which you expect to be either an object or a collection. There are further actions you want to take but only if the parameter is not empty. Normally you need to do two tests:

var $var : Variant

Case of 
	: (Value type($var)=Is collection)
		If ($var.length>0)
			// do this
		Else 
			// do something esle
		End if 
		
	: (Value type($var)=Is object)
		If (OB Is empty($var))
			// do something esle
		Else 
			// do this
		End if 
		
  Else
  //  whatever
End case 

Using nvl you can do this:

Case of 
	: (nvl($var;Is collection;New collection).length>0)
		//  do this
		
	: (OB Keys(nvl($var;Is object;New object)).length>0)
		//  do this
		
	Else 
		// whatever
		
End case 

In both cases I specify an empty instance of the expected value as the null return value. This way I can do both tests in one call.

Specifying the null return also helps when I want a zero value instead of Null. For example

$newValue:=nvl($var;Is real;0)

If $var is null $newValue will be zero. But perhpas I want to know which values are null but also want the values to all be real so I'm going to use -1 as my null value:

$newValue:=nvl($var;Is real;-1)

nvl also does some simple transformations.

$var:="123.45"  //  text var
$newValue:=nvl($var;Is real;-1) //  $newValue = 123.45  real value

Take a look at the nvl_unit_tests for more examples.

This database is written in v18R4. It may work in prior versions but I haven't tested it there.