nv.1

test.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+declare -A array
+array[x1,y1]=100
+array[x1,y2]=200
+array[x2,y1]=300
+array[x2,y2]=400
+#alternative 1, extract all the main keys with sort
+for key in $(printf '%s\n' "${!array[@]}" | sed 's/,.*//' | sort -u); do
+#alternative 2, keeping track of the main keys
+keys=(x1 x2)
+for key in "${keys[@]}"; do
+
+    #the loop contents are the same
+    echo "$key : y1 = ${array[$key,y1]}"
+    echo "$key : y2 = ${array[$key,y2]}"
+done