expressions

Expressions

An expression can be specified as the value of the filter property on certain layers or to define some of their options. They are represented as JSON array.

Some fields on the layer's options accept either an expression or a value, for example a string or a number. For example, the FillColor property of the PolygonExtrusionLayerOptions is of type ExpressionOrString. The constructor of the ExpressionOrString class allows to give either :

• A string representing the expression.
• Subexpressions which will be combined to build the expression.
• A JsonDocument representing the expression.

The ExpressionOrNumber and ExpressionOrStringArray classes offers the same possibilities with different types, respectively double? and IEnumerable<string>.

The Expression class only offers the possiblity to combine expressions or use a JsonDocument.

For more information on the Expressions, take a look at the Web SDK Documentation.

Examples

The following examples show you the multiple ways to set the FillColor of the PolygonExtrusionLayerOptions.

Using a value

The following example would fill the entire layer with a red color :

var layer = new AzureMapsControl.Components.Layers.PolygonExtrusionLayer
{
    Options = new Components.Layers.PolygonExtrusionLayerOptions
    {
        FillColor = new Components.Atlas.ExpressionOrString("red")
    }
};

Checking if property exists

A necessity to check if property has value to decide which value to pick during clustering (or data display):

var expression = Expression.HasProperty("score");

Property value getter

Similarly get property value can be fetched:

var leafProp = Expression.GetProperty("leafValue");

Double is treated as ExpressionOrNumber

A portion of APIs require an expression to be evaluated to number, like bubble radius. Since ExpressionOrNumber has implicit cast from double?, you can simply specify number:

ExpressionOrNumber smallRadius = 10;

Converting Expression to ExpressionOrNumber

When expression evaluates to number, but is represented as general-purpose Expression type, call .ToNumber() to apply to-number` cast expression:

Expression alreadyNumber = new ExpressionOrNumber(5); // expression variable is a number for sure
ExpressionOrNumber expression = alreadyNumber.ToNumber(); 

More examples

More API samples can be found in Expressions Unit Test block.

Using expressions

The following example would fill the layer with a color based on the DENSITY property of the layer source :

var layer = new AzureMapsControl.Components.Layers.PolygonExtrusionLayer
        {
            Options = new Components.Layers.PolygonExtrusionLayerOptions
            {
                FillColor = new Components.Atlas.ExpressionOrString(new AzureMapsControl.Components.Atlas.Expression[] {
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("step"),
                    new AzureMapsControl.Components.Atlas.Expression(new AzureMapsControl.Components.Atlas.Expression[]{
                        new AzureMapsControl.Components.Atlas.ExpressionOrString("get"),
                        new AzureMapsControl.Components.Atlas.ExpressionOrString("DENSITY")
                    }),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#00ff80"),
                    new AzureMapsControl.Components.Atlas.ExpressionOrNumber(10),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#09e076"),
                    new AzureMapsControl.Components.Atlas.ExpressionOrNumber(20),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#0bbf67"),
                    new AzureMapsControl.Components.Atlas.ExpressionOrNumber(50),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#f7e305"),
                    new AzureMapsControl.Components.Atlas.ExpressionOrNumber(100),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#f7c707"),
                    new AzureMapsControl.Components.Atlas.ExpressionOrNumber(200),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#f78205"),
                    new AzureMapsControl.Components.Atlas.ExpressionOrNumber(500),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#f75e05"),
                    new AzureMapsControl.Components.Atlas.ExpressionOrNumber(1000),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#f72505"),
                    new AzureMapsControl.Components.Atlas.ExpressionOrNumber(10000),
                    new AzureMapsControl.Components.Atlas.ExpressionOrString("#6b0a05")
                }),
            }
        };

Using a JSON Document

The following example has the same result as the one using the expressions, but uses the JSON representation of the expression :

var fillColorExpressionJsonString = "[\"step\", [\"get\", \"DENSITY\"], \"#00ff80\", 10, \"#09e076\", 20, \"#0bbf67\", 50, \"#f7e305\", 100, \"#f7c707\", 200, \"#f78205\", 500, \"#f75e05\", 1000, \"#f72505\", 10000, \"#6b0a05\"]";

var layer = new AzureMapsControl.Components.Layers.PolygonExtrusionLayer
{
    Options = new Components.Layers.PolygonExtrusionLayerOptions
    {
        FillColor = new Components.Atlas.ExpressionOrString(System.Text.Json.JsonDocument.Parse(fillColorExpressionJsonString))
    }
};