more generalisation of commonly used code constructs

include/text.php

@@ -3261,3 +3261,31 @@ function purify_filename($s) {
 		return '';
 	return $s;
 }
+
+
+/**
+ * @brief array_elm_to_str($arr,$elm,$delim = ',') extract unique individual elements from an array of arrays and return them as a string separated by a delimiter
+ *  
+ * empty elements (evaluated after trim()) are ignored.
+ * @param $arr array
+ * @param $elm array key to extract from sub-array
+ * @param $delim string default ','
+ * @returns string
+ */
+
+function array_elm_to_str($arr,$elm,$delim = ',') {
+
+	$tmp = [];
+	if($arr && is_array($arr)) {
+		foreach($arr as $x) {
+			if(is_array($x) && array_key_exists($elm,$x)) {
+				$z = trim($x[$elm]);
+				if(($z) && (! in_array($z,$tmp))) {
+					$tmp[] = $z;
+				}
+			}
+		}
+	}
+	return implode($tmp,$delim);
+}
+