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Data Mapping > Data Mapper Functions > By Category > Aggregate > Min

Glossary Item Box

Function Name
Min
Category
Aggregate
Icon
Min
Description
Retrieve the minimum value within a context
Inputs
Context Context within which to determine minimum value [optional]
Value Value to retrieve minimum instance of
Outputs
Result Minimum value found within context
Properties
None -

Usage

The Data Mapper Aggregate Min function allows you to retrieve minimum values within specific contexts. The Context input is optional, so you can simply retrieve the minimum value for the whole data source by not connecting it. If you do connect the Context input, the minimum is taken within the specified parent node. To apply the Aggregate Min function, use the following process:

Create a new Data Mapper file, dragging your XML data source and targets into the editor area. For this example we are using sellers_source.xsd, an XML Schema Definition inferred from the following source:

Source XML Copy Code
<sellers>
 <salesperson>
  <name>John Davidson</name>
  <sales>12800</sales>
 </salesperson>
 <salesperson>
  <name>Jane Johnson</name>
  <sales>23050</sales>
 </salesperson>
 <salesperson>
  <name>Mark Smith</name>
  <sales>18200</sales>
 </salesperson>
</sellers>

For our target schema we will be using sellers_target.xsd, inferred from the following XML:

Target XML Copy Code
<sales_staff>
 <sales_data type="min">23700</sales_data>
 <sales_assistant seller_name="Ken Jameson">
  <amount>34020</amount>
 </sales_assistant>
 <sales_assistant seller_name="Lisa Matthews">
  <amount>27500</amount>
 </sales_assistant>
 <sales_assistant seller_name="Paul Norton">
  <amount>23700</amount>
 </sales_assistant>
</sales_staff>

The data models sales for individual salespeople within a retail organisation. Let's assume that, as well as mapping the salespeople and their data, we also want to determine the minimum sales figure across all staff members. We will record this in the "sales_data" element together with a String indicating the type of data we are recording as in the target above. Here is the Data Mapper with Source and Target imported:

Data Mapper Source and Target

Drag the Aggregate Min function from the Component Palette into the mapping area:

Aggregate Min Component

Min Added

The Min function takes two inputs, representing the value to retrieve the minimum instance of and the context in which it should be calculated as minimum. Both inputs and output of the Min function may be connected to items in the XML Reader/ Writer or other components in the Mapper.

Connect the Context input of the Min function to the "sellers" output in the XML Reader and the Value input to the "sales" output.

Reader to Min

This will output the minimum sales across all sellers. In this case, the effect would be the same if we did not connect the Context input, however if we had categories of sellers, for example in different stores, we would perhaps want to calculate the minimum sales for each store. Connect the Min output to the "Element Value" within the "sales_data" element in the XML Writer.

Min to Writer

This will ensure that the "sales_data" element is written out with the minimum sales value inside it each time the data is mapped.

Now we need to define the type of data we are including in the "sales_data" element. Drag a Constant Value from the Data Type section onto the Mapper. Right-click it and choose Show Properties. Choose a String Data Type enter "min" as the Value, or anything else you prefer.

Constant Properties

Connect the Constant output to the "type" input in the XML Writer.

Constant to Writer

Finally let's make the remaining input and output connections. Remember to map "sellers" to "sales_staff" and "sales" to "amount" - although we have used these as references we have not yet mapped them. We do not need to map anything to the "sales_data" element input as the Element Value will ensure the element itself is mapped.

Inputs and Outputs Connected

We can now execute the transform by pressing Shift-F5 or the Execute button (Execute). The transform is applied and the file we selected as output opens in the editor:

Output XML Copy Code
<sales_staff>
 <sales_data type="min">12800</sales_data>
 <sales_assistant seller_name="John Davidson">
  <amount>12800</amount>
 </sales_assistant>
 <sales_assistant seller_name="Jane Johnson">
  <amount>23050</amount>
 </sales_assistant>
 <sales_assistant seller_name="Mark Smith">
  <amount>18200</amount>
 </sales_assistant>
</sales_staff>

The output contains the data values mapped from the source and the minimum sales value included in the new "sales_data" element, together with a String indicating the meaning of the value.

If you do not connect the Context input of the Min function, the result will be the minimum for the data source as a whole.

See Also