diff --git a/README.md b/README.md
index ad39d19..22f0ce0 100644
--- a/README.md
+++ b/README.md
@@ -88,27 +88,27 @@ argument is not supplied the accumulator is initialised to `0`.
 lume.reduce({1, 2, 3}, function(a, b) return a + b end) -- Returns 6
 ```
 
-### lume.set(t, [, isarray])
+### lume.set(t, [, retainkeys])
 Returns a copy of the `t` table with all the duplicate values removed. If
-`isarray` is true the table is treated as an array.
+`retainkeys` is true the table is not treated as an array and retains its
+original keys.
 ```lua
 lume.set({2, 1, 2, "cat", "cat"}) -- Returns {1, 2, cat}
 ```
 
-### lume.filter(t, fn [, isarray])
-Iterates the table `t` and calls `fn` on each value. Returns a new table with
-only the value which `fn` returned true. If `isarray` is true the table is
-treated as an array, `isarray` is false by default.
+### lume.filter(t, fn [, retainkeys])
+Calls `fn` on each value of `t` table. Returns a new table with only the values
+where `fn` returned true. If `retainkeys` is true the table is not treated as
+an array and retains its original keys.
 ```lua
 lume.filter({1, 2, 3, 4}, function(x) return x % 2 == 0 end, true) 
 -- Returns {2, 4}
 ```
 
-### lume.merge(t, t2 [, isarray])
-Merges all the values from the table `t2` into `t` in place. If `isarray` is
-true the tables are treated as arrays, `isarray` is false by default. If
-`isarray` is false and `t` and `t2` have a conflicting key, the value from `t2`
-is used.
+### lume.merge(t, t2 [, retainkeys])
+Merges all the values from the table `t2` into `t` in place. If `retainkeys` is
+true the table is not treated as an array and retains its original keys; if `t`
+and `t2` have a conflicting key, the value from `t2` is used.
 ```lua
 lume.merge({2, 3}, {4, 5}, true) -- Returns {2, 3, 4, 5}
 ```
diff --git a/lume.lua b/lume.lua
index ccf4f02..812a759 100644
--- a/lume.lua
+++ b/lume.lua
@@ -110,29 +110,27 @@ function lume.reduce(t, fn, first)
 end
 
 
-function lume.set(t, isarray)
+function lume.set(t, retainkeys)
   local tmp = {}
   for k, v in pairs(t) do tmp[v] = k end
   local rtn = {}
-  for k, v in pairs(tmp) do 
-    rtn[isarray and (#rtn + 1) or v] = k
-  end
+  for k, v in pairs(tmp) do rtn[retainkeys and v or (#rtn + 1)] = k end
   return rtn
 end
 
 
-function lume.filter(t, fn, isarray)
+function lume.filter(t, fn, retainkeys)
   local rtn = {}
   for k, v in pairs(t) do
-    if fn(v) then rtn[isarray and (#rtn + 1) or k] = v end
+    if fn(v) then rtn[retainkeys and k or (#rtn + 1)] = v end
   end
   return rtn
 end
 
 
-function lume.merge(t, t2, isarray)
+function lume.merge(t, t2, retainkeys)
   for k, v in pairs(t2) do
-    t[isarray and (#t + 1) or k] = v
+    t[retainkeys and k or (#t + 1)] = v
   end
   return t
 end