QGIS/resources/function_help/json/array_to_string

{
  "name": "array_to_string",
  "type": "function",
  "description": "Concatenates array elements into a string separated by a delimiter and using optional string for empty values.",
  "arguments": [
    {"arg":"array", "description":"the input array"},
    {"arg":"delimiter","optional":true,"default":"','","description":"the string delimiter used to separate concatenated array elements"},
    {"arg":"empty_value","optional":true,"default":"''","description":"the optional string to use as replacement for empty (zero length) matches"}],
  "examples": [ { "expression":"array_to_string(array('1','2','3'))", "returns":"'1,2,3'"},
                { "expression":"array_to_string(array(1,2,3),'-')", "returns":"'1-2-3'"},
                { "expression":"array_to_string(array('1','','3'),',','0')", "returns":"'1,0,3'"}
  ]
}