Apply Expression – Avenza Systems

Use the Apply Expression function to assign new values or edit attribute properties. For example, it can be used to compute attribute values based on the values in other columns, to assign a style by editing the #Style property attribute or to rotate symbols by assigning a fixed value to the #Rotation property attribute. Read-only attributes cannot be edited with Apply Expression.

Note that property attributes are dynamic. Changes made to them in the map attribute table are reflected immediately in the graphical properties and on-screen display of the data to which they are linked. Expressions can be generated and applied to data based on the values found in an existing attribute column, providing a one-step process to transform a vast number of different objects in a single operation.

information Unlike the Derive Value From Expression option in Edit Schema, values computed through Apply Expression are not tied to the original attributes constructing the expression and can be edited later on. Only currently selected artwork is affected by the changes.

Using Apply Expressions

Ensure the data required for the application of the expression is selected and appears in the MAP Attributes panel. Click the Apply Expression button or choose it from the panel options menu.

applyexpression_dialog

First, specify a column from the Apply to list to specify which attribute column the expression will be applied to. The columns listed here are representative of the attribute structure unique to the data layer currently displayed in the attribute table as well as the standard MAPublisher property attributes.

To assign an expression to a column, enter a valid expression in the Expression text box. Alternatively, click the Expression Builder button to open the Expression Builder dialog box. To access other expressions saved in the map document, click the Expression Library button to open the Expression Library dialog box.

The Expression Validity icon will report if the expression entered is valid (green checkmark). Otherwise, it will report invalid (red exclamation) and include additional warning notes.