September 2017 Update

Task/Sort-using-a-custom-comparator/Jq/sort-using-a-custom-comparator-1.jq

@@ -0,0 +1,22 @@
+def quicksort(cmp):
+  if length < 2 then .                                     # it is already sorted
+  else .[0] as $pivot
+    | reduce .[] as $x
+      # state: [less, equal, greater]
+      ( [ [], [], [] ];                                    # three empty arrays:
+        if   $x == $pivot then    .[1] += [$x]             # add x to equal
+        else ([$x,$pivot]|cmp) as $order
+          | if   $order == 0 then .[1] += [$x]             # ditto
+            elif ($order|type) == "number" then
+              if $order < 0 then  .[0] += [$x]             # add x to less
+              else .[2] += [$x]                            # add x to greater
+              end
+            else ([$pivot,$x]|cmp) as $order2
+              | if $order and $order2 then   .[1] += [$x]  # add x to equal
+                elif $order then   .[0] += [$x]            # add x to less
+                else .[2] += [$x]                          # add x to greater
+                end
+            end
+        end )
+    | (.[0] | quicksort(cmp) ) + .[1] + (.[2] | quicksort(cmp) )
+  end ;

Task/Sort-using-a-custom-comparator/Jq/sort-using-a-custom-comparator-2.jq

@@ -0,0 +1,3 @@
+# Sort by string length, breaking ties using ordinary string comparison.
+["z", "yz", "ab", "c"]
+  | quicksort( (.[0]|length) > (.[1]|length) or ( (.[0]|length) == (.[1]|length) and .[0] < .[1] ) )

Task/Sort-using-a-custom-comparator/Jq/sort-using-a-custom-comparator-3.jq

@@ -0,0 +1,6 @@
+[
+  "ab",
+  "yz",
+  "c",
+  "z"
+]