On both sides, you can edit all expression keys of input/output data or filtering conditions by using Pig Latin. This allows you to filter or split a relation on the basis of those conditions. For details about Pig Latin and a relation in Pig, see Apache's documentation about Pig such as Pig Latin Basics and Pig Latin Reference Manual.
You can write the expressions necessary for the data transformation directly in the Expression editor view located in the lower half of the expression editor, or you can open the [Expression Builder] dialog box where you can write the data transformation expressions.
To open the [Expression Builder] dialog box, click the button next to the expression you want to open in the tabular panels representing the lookup flow(s) or the output flow(s) of the Map Editor.
The [Expression Builder] dialog box opens on the selected expression.
If you have created any Pig user-defined function (Pig UDF) in the Studio, a Pig UDF Functions option appears automatically in the Categories list and you can select it to edit the mapping expression you need to use.
You need to use the Pig UDF item under the Code node of the Repository tree to create a Pig UDF function. Although you need to know how to write a Pig function using Pig Latin, a Pig UDF function is created the same way as a Talend routine.
Note that your Repository may look different from this image depending on the license you are using.
For further information about a routine, see Managing routines.
To open the Expression editor view,
In the lower half of the editor, click the Expression editor tab to open the corresponding view.
Click the column you need to set expressions for and edit the expressions in the Expression editor view.
If you need to set filtering conditions for an input or output flow, you have to click the button and then edit the expressions in the displayed area or by using the Expression editor view or the [Expression Builder] dialog box.