Expressions

Expressions can be used in various places in the form metadata file.

They are implemented using the expression evaluator library: https://github.com/silentmatt/expr-eval

Variables in expressions are bound to the data model and the supported operators are described in the documentation of the library.

e.g

{
    "dataType":"number",
    "name":"example",
    "computed": {
        "expression":"value1+value2*3"
    }
}

In addition to the library supported operators, there are a few functions that work on list (array) data types. These are: sum, count, any, none, all.

Each of these functions takes an array as the first argument and a string expression as the second. The expression will be evaluated against each element of the array.

e.g.

{
    "dataType":"list",
    "name":"listData",
    "columns":[...]
},
{
    "dataType":"number",
    "name":"example",
    "computed":{
        "expression":"sum(listData, \"value1+value2\")"
    }
}

nb when using string literals in expressions, use double quotes not single quotes.