Symbology with Arcade Expression using ArcGIS Pro

Question

I am using ArcGIS Pro 2.6.

I have a line feature class, in the attributes of which there is a field "Type", and "Thickness", I need to make a complex Symbology that unites these 2 fields.

It would seem an easy task, but the lines are constantly updated and the values in the "Thickness" field as well. I need to make sure that the "Thickness" field is graded, such as from 0 - 2, 2.5-4, etc. and at the same time it was merged with the "Type" field as in the picture

Script:

var w = $feature.Thickness
var width_str

// Here we define the width classification ranges
if(w < 0.8){
    width_str = ' up to 0.8'
} else if (w < 2) {
    width_str = ' between 0.8 and 2'}
} else if (w = Null) {
    width_str = ' '}

return $feature.Type + width_str

I have error:

General parsing error

What causes that?

Answer 1

Beyond the parsing error, there is a larger issue with the handling of null values. Arcade, similar to JavaScript and some other languages, will cast null to 0 when casting to numeric for use with comparison operators. Under the current logic of the code, a null value will result in the first conditional check as being true, and hence null will get a label of ' up to 0.8' instead of an empty string.

Before getting into ways of addressing null values, I want to point out that many languages have specific functions for evaluating series of conditional expressions so that long if/else statements are not needed. In the case of Arcade the function is When | ArcGIS Arcade | ArcGIS Developers, and I will rewrite the code using it.

Getting back to null values, there are at least a couple different ways to handle them. One approach is to use Default Value | ArcGIS Arcade | ArcGIS Developers to check for null (or empty string) and set it to infinity, which will allow the current code logic to work.

var w = DefaultValue($feature.Thickness, Infinity);
var width_str;

// Here we define the width classification ranges
When(
    w < 0.8, width_str = ' up to 0.8',
    w < 2, width_str = ' between 0.8 and 2',
    ' '
);

return $feature.Type + width_str;

Another approach is to put the IsEmpty | ArcGIS Arcade | ArcGIS Developers check first to handle null.

var w = $feature.Thickness;
var width_str;

// Here we define the width classification ranges
When(
    IsEmpty(w), ' ',
    w < 0.8, width_str = ' up to 0.8',
    w < 2, width_str = ' between 0.8 and 2',
    ' '
);

return $feature.Type + width_str